tcp: Update MIB counters for drops

This patch updates LINUX_MIB_LISTENDROPS in tcp_v4_conn_request() and
tcp_v4_err(). tcp_v4_conn_request() in particular can drop SYNs for various
reasons which are not currently tracked.

Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 629937d..eadb693 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -496,6 +496,7 @@
 		 * errors returned from accept().
 		 */
 		inet_csk_reqsk_queue_drop(sk, req, prev);
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
 		goto out;
 
 	case TCP_SYN_SENT:
@@ -1502,7 +1503,6 @@
 	 */
 	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
-		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
 		goto drop;
 	}
 
@@ -1669,6 +1669,7 @@
 drop_and_free:
 	reqsk_free(req);
 drop:
+	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
 	return 0;
 }
 EXPORT_SYMBOL(tcp_v4_conn_request);