This commit adds a number of fixes to the OpenVPN up/down hotplug command
wrapper which currently fails to actually invoke user defined up and down
commands for uci configurations not using external native configurations.

 - Use the `--setenv` to pass the user configured `up` and `down` commands
   as `user_up` and `user_down` environment variables respectively

 - Instead of attempting to scrape the `up` and `down` settings from the
   (possibly generated) native OpenVPN configuration in
   `/etc/hotplug.d/openvpn/01-user`, read them from the respective
   environment variables instead

 - Fix parsing of native configuration values in `get_openvpn_option()`;
   first try to parse a given setting as single quoted value, then as
   double quoted and finally as non-quoted, potentially white-space
   escaped one. This ensures that `up '/bin/foo'` is interpreted as
   `/bin/foo` and not `'/bin/foo'`

Ref: https://forum.openwrt.org/t/openvpn-up-down-configuration-ignored/91126
Supersedes: #15121, #15284
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

See https://www.mankier.com/8/openvpn#--server-poll-timeout

Signed-off-by: Alexander Egorenkov <egorenar-dev@posteo.net>

Some VPN providers require username and password for client to connect.
This commit adds an option to specify username, password and
cert_password directly in uci config which then gets expanded during
start of openpvn client.

Signed-off-by: Michal Hrusecky <michal.hrusecky@turris.com>

OpenVPN recommends disabling compression, as it may weaken the security
of the connection. For users who need compression, we build with LZ4
support by default. LZO in OpenVPN pulls in liblzo at approx. 32 kB.

OpenWrt users will no longer be able to connect to OpenVPN peers that
require LZO compression, unless they build the OpenVPN package themselves.

Signed-off-by: Magnus Kroken <mkroken@gmail.com>

New features:
* Per client tls-crypt keys
* ChaCha20-Poly1305 can be used to encrypt the data channel
* Routes are added/removed via Netlink instead of ifconfig/route
  (unless iproute2 support is enabled).
* VLAN support when using a TAP device

Significant changes:
* Server support can no longer be disabled.
* Crypto support can no longer be disabled, remove nossl variant.
* Blowfish (BF-CBC) is no longer implicitly the default cipher.
  OpenVPN peers prior to 2.4, or peers with data cipher negotiation
  disabled, will not be able to connect to a 2.5 peer unless
  option data_fallback_ciphers is set on the 2.5 peer and it contains a
  cipher supported by the client.

Signed-off-by: Magnus Kroken <mkroken@gmail.com>

Signed-off-by: Rosen Penev <rosenp@gmail.com>