netfilter: nf_nat: change sequence number adjustments to 32 bits

Using 16 bits is too small, when many adjustments happen the offsets might
overflow and break the connection.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 7dcc376..8f308d8 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -496,7 +496,7 @@
 }
 
 #ifdef CONFIG_NF_NAT_NEEDED
-static inline s16 nat_offset(const struct nf_conn *ct,
+static inline s32 nat_offset(const struct nf_conn *ct,
 			     enum ip_conntrack_dir dir,
 			     u32 seq)
 {
@@ -525,7 +525,7 @@
 	struct ip_ct_tcp_state *receiver = &state->seen[!dir];
 	const struct nf_conntrack_tuple *tuple = &ct->tuplehash[dir].tuple;
 	__u32 seq, ack, sack, end, win, swin;
-	s16 receiver_offset;
+	s32 receiver_offset;
 	bool res;
 
 	/*