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.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/ipv4/netfilter/nf_nat_irc.c b/net/ipv4/netfilter/nf_nat_irc.c
index 979ae16..5b0c20a 100644
--- a/net/ipv4/netfilter/nf_nat_irc.c
+++ b/net/ipv4/netfilter/nf_nat_irc.c
@@ -29,6 +29,7 @@
 
 static unsigned int help(struct sk_buff *skb,
 			 enum ip_conntrack_info ctinfo,
+			 unsigned int protoff,
 			 unsigned int matchoff,
 			 unsigned int matchlen,
 			 struct nf_conntrack_expect *exp)
@@ -66,7 +67,7 @@
 		 buffer, &ip, port);
 
 	ret = nf_nat_mangle_tcp_packet(skb, exp->master, ctinfo,
-				       matchoff, matchlen, buffer,
+				       protoff, matchoff, matchlen, buffer,
 				       strlen(buffer));
 	if (ret != NF_ACCEPT)
 		nf_ct_unexpect_related(exp);