Fixes #1830

remember that PeerSet#Get can return nil

except now we calculate the max size using the maxPacketMsgSize()
function, which frees developers from having to know amino encoding
details.

plus, 10 additional bytes are added to leave the room for amino upgrades
(both making it more efficient / less efficient)

Fixes #1762#issuecomment-398940107

* update changelog

* document p2p/listener

* do not expose underlying net.Listener

* add a TODO

* replace todo with a comment

* config: rename skip_upnp to upnp

Change default option to enable upnp.

Closes #1806

* doc updates

- fix comment and set UPNP to false in TestP2PConfig
- add UPNP to config template
- update changelog

- re-add test
- add TODO
- err instead of panic where possible

This reverts commit 96a3502

- move prometheus metrics into internal packages
- *Option structs
- misc. format changes

* Switch ports 466xx to be 266xx
This is done so the default ports aren't in the linux kernel's default ephemeral port range.

* Update ABCI import

* Bump cache on circleci

* Get more verbose output for debugging

* Bump abci dependency

* Fix accidental change of a block header's hash

* pin abci release

```
I[06-08|11:51:57.234] Getting UPNP external address                module=p2p
I[06-08|11:51:58.867] Got UPNP external address                    module=p2p address=
```

Fixes #1717

```
I[06-08|11:51:56.952] Starting multiAppConn                        module=proxy impl=multiAppConn
I[06-08|11:51:56.952] Starting localClient                         module=abci-client connection=query impl=localClient
I[06-08|11:51:56.952] Starting localClient                         module=abci-client connection=mempool impl=localClient
I[06-08|11:51:56.952] Starting localClient                         module=abci-client connection=consensus impl=localClient
I[06-08|11:51:56.952] ABCI Handshake                               module=consensus appHeight=0 appHash=
I[06-08|11:51:56.952] ABCI Replay Blocks                           module=consensus appHeight=0 storeHeight=0 stateHeight=0
I[06-08|11:51:57.053] Completed ABCI Handshake - Tendermint and App are synced module=consensus appHeight=0 appHash=
I[06-08|11:51:57.053] This node is a validator                     module=consensus addr=6816B5D9BAC32A3CDF07884D9D3D2650694C371D pubKey=PubKeyEd25519{27A40CD032DD2467342D0CF27C5EC92052D966FEC714B6CF2F3BF3146AFD0D51}
I[06-08|11:51:57.234] Starting Node                                module=main impl=Node
I[06-08|11:51:57.234] Starting EventBus                            module=events impl=EventBus
I[06-08|11:51:57.234] Local listener                               module=p2p ip=:: port=46656
I[06-08|11:51:57.234] Getting UPNP external address                module=p2p
I[06-08|11:51:58.867] Got UPNP external address                    module=p2p address=
I[06-08|11:51:58.867] Starting DefaultListener                     module=p2p impl=Listener(@<nil>:46656)
I[06-08|11:51:58.867] P2P Node ID                                  module=main ID=3629b516392e494ae717ac4c6a1ea7eb0fe421c3 file=/home/tpb/.tendermint/config/node_key.json
I[06-08|11:51:58.868] Add our address to book                      module=p2p book=/home/tpb/.tendermint/config/addrbook.json addr=null
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x38 pc=0x89fb86]

goroutine 1 [running]:
github.com/tendermint/tendermint/p2p.(*NetAddress).String(0x0, 0xc96e24, 0x17)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/p2p/netaddress.go:171 +0x26
github.com/tendermint/tendermint/p2p/pex.(*addrBook).AddOurAddress(0xc420190620, 0x0)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/p2p/pex/addrbook.go:160 +0x116
github.com/tendermint/tendermint/node.(*Node).OnStart(0xc420286d00, 0xc4201b8010, 0xd)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/node/node.go:402 +0x547
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common.(*BaseService).Start(0xc420286d00, 0xe51c40, 0xc42000bd40)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common/service.go:130 +0x3bd
github.com/tendermint/tendermint/cmd/tendermint/commands.NewRunNodeCmd.func1(0xc42022e000, 0xc4200acdc0, 0x0, 0x1, 0x0, 0x0)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/cmd/tendermint/commands/run_node.go:58 +0xfe
github.com/tendermint/tendermint/vendor/github.com/spf13/cobra.(*Command).execute(0xc42022e000, 0xc4200acda0, 0x1, 0x1, 0xc42022e000, 0xc4200acda0)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/vendor/github.com/spf13/cobra/command.go:762 +0x468
github.com/tendermint/tendermint/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0x1289280, 0xbbdda0, 0xc420015e01, 0xc4201bc640)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/vendor/github.com/spf13/cobra/command.go:852 +0x30a
github.com/tendermint/tendermint/vendor/github.com/spf13/cobra.(*Command).Execute(0x1289280, 0xc4201bc640, 0xc420015e98)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/vendor/github.com/spf13/cobra/command.go:800 +0x2b
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/cli.Executor.Execute(0x1289280, 0xde5798, 0x2, 0xc4200332c0)
	/home/tpb/code/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/cli/setup.go:89 +0x4e
main.main()
	/home/tpb/code/go/src/github.com/tendermint/tendermint/cmd/tendermint/main.go:45 +0x24d
```

Instead of mutating the passed in MConnConfig part of P2PConfig we just
use the default and override the values, the same as before as it was
always the default version. This is yet another good reason to not embed
information and access to config structs in our components and will go
away with the ongoing refactoring in #1325.

Fixes https://github.com/cosmos/cosmos-sdk/issues/1045

As both configs are concerned with the p2p packaage and PeerConfig is
only used inside of the package there is no good reason to keep the
couple of fields separate, therefore it is collapsed into the more
general P2PConifg. This is a stepping stone towards a setup where the
components inside of p2p do not have any knowledge about the config.

follow-up to #1325

As we didn't hear any voices requesting this feature, we removed the
option to disable it and always have peer connection auth encrypted.

closes #1518
follow-up #1325

In some scenarios like tests we want to disable the guard which prevents
peers connecting from the same ip.

Fixes #1632
Closes #1634

BEFORE:

```
E[05-24|11:55:37.229] Dialing failed                               pex=0 addr=022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593 err="Connect to self: <nil>" attempts=0
```

AFTER:

```
E[05-24|11:55:37.229] Dialing failed                               pex=0 addr=022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593 err="Connect to self: 022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593" attempts=0
```

Closes #1227