netfilter: add protocol independent NAT core

Convert the IPv4 NAT implementation to a protocol independent core and
address family specific modules.

Change-Id: I926b42af53b37c96fb654021e7f568450e8c63c0
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
52 files changed