netfilter: conntrack: increase drop stats if sequence adjustment fails

This patch increases the statistics of packets drop if the sequence
adjustment fails in ipv4_confirm().
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c

@@ -120,8 +120,10 @@ static unsigned int ipv4_confirm(unsigned int hooknum,
 		typeof(nf_nat_seq_adjust_hook) seq_adjust;
 
 		seq_adjust = rcu_dereference(nf_nat_seq_adjust_hook);
-		if (!seq_adjust || !seq_adjust(skb, ct, ctinfo))
+		if (!seq_adjust || !seq_adjust(skb, ct, ctinfo)) {
+			NF_CT_STAT_INC_ATOMIC(nf_ct_net(ct), drop);
 			return NF_DROP;
+		}
 	}
 out:
 	/* We've seen it coming out the other side: confirm it */