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_ftp.c b/net/ipv4/netfilter/nf_nat_ftp.c
index e462a95..5589f3a 100644
--- a/net/ipv4/netfilter/nf_nat_ftp.c
+++ b/net/ipv4/netfilter/nf_nat_ftp.c
@@ -55,6 +55,7 @@
 static unsigned int nf_nat_ftp(struct sk_buff *skb,
 			       enum ip_conntrack_info ctinfo,
 			       enum nf_ct_ftp_type type,
+			       unsigned int protoff,
 			       unsigned int matchoff,
 			       unsigned int matchlen,
 			       struct nf_conntrack_expect *exp)
@@ -100,7 +101,7 @@
 
 	pr_debug("calling nf_nat_mangle_tcp_packet\n");
 
-	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
+	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
 				      matchlen, buffer, buflen))
 		goto out;