netfilter: nf_nat: add protoff argument to packet mangling functions

For mangling IPv6 packets the protocol header offset needs to be known
by the NAT packet mangling functions. Add a so far unused protoff argument
and convert the conntrack and NAT helpers to use it in preparation of
IPv6 NAT.

Change-Id: I8910efcf9411b509a065cf84e8277d1d04315700
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
22 files changed