[NETFILTER] NAT sequence adjustment: Save eight bytes per conntrack

This patch reduces the size of 'struct ip_conntrack' on systems with NAT
by eight bytes.  The sequence number delta values can be int16_t, since
we only support one sequence number modification per window anyway, and
one such modification is not going to exceed 32kB ;)
Signed-off-by: NHarald Welte <laforge@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netfilter_ipv4/ip_nat.h

@@ -23,7 +23,7 @@ struct ip_nat_seq {
 	 * modification (if any) */
 	u_int32_t correction_pos;
 	/* sequence number offset before and after last modification */
-	int32_t offset_before, offset_after;
+	int16_t offset_before, offset_after;
 };
 
 /* Single range specification. */