The next OpenWrt stable release aims to use firewall4 by default. As
this uses nftables as backend, miniupnpd will no longer work. Create an
iptables and nftables variant of the miniupnpd package so that miniupnpd
can be used with either firewall variant.

See #16818 for more info.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

Import miniupnpd from routing repo and bump to 20180422.

Drop 102-ipv6-ext-port.patch as this looks upstreamed in the pinhole
code to me.
Consolidate all other patches & update with a view to sending upstream.

Add support for runtime IGDv1 mode switch (default to IGDv2)

(not extensively) Tested-on: ar71xx Archer C7 v2 in IGDv1 compatibility
mode.  A variety of devices/applications appear to be able to create
mappings.

Have an attempt at resolving https://github.com/openwrt-routing/packages/issues/286
TL;DR miniupnpd rules get processed before fw3 rules and thus can
override existing/intended redirects.  Ideally the miniupnpd rules would
be last in the relevant chains, unfortunately fw3 can sometimes use the
last rule as a REJECT.  Put miniupnpd rules as penultimate.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>