tcp: ipv6: Update MIB counters for drops

This patch updates LINUX_MIB_LISTENDROPS and LINUX_MIB_LISTENOVERFLOWS in
tcp_v6_conn_request() and tcp_v6_err(). tcp_v6_conn_request() in particular can
drop SYNs for various reasons which are not currently tracked.
Signed-off-by: NVijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

@@ -423,6 +423,7 @@ static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		}
 
 		inet_csk_reqsk_queue_drop(sk, req, prev);
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
 		goto out;
 
 	case TCP_SYN_SENT:
@@ -958,8 +959,10 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 			goto drop;
 	}
 
-	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)
+	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
 		goto drop;
+	}
 
 	req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
 	if (req == NULL)
@@ -1108,6 +1111,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 drop_and_free:
 	reqsk_free(req);
 drop:
+	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
 	return 0; /* don't send reset */
 }