udp: Add MIB counters for rcvbuferrors

Add MIB counters for rcvbuferrors in UDP to help diagnose problems.

Signed-off-by: James M Leddy <james.leddy@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 95c8347..7092ff7 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -674,8 +674,11 @@
 			goto csum_error;
 	}
 
-	if (sk_rcvqueues_full(sk, skb, sk->sk_rcvbuf))
+	if (sk_rcvqueues_full(sk, skb, sk->sk_rcvbuf)) {
+		UDP6_INC_STATS_BH(sock_net(sk),
+				  UDP_MIB_RCVBUFERRORS, is_udplite);
 		goto drop;
+	}
 
 	skb_dst_drop(skb);
 
@@ -690,6 +693,7 @@
 	bh_unlock_sock(sk);
 
 	return rc;
+
 csum_error:
 	UDP6_INC_STATS_BH(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
 drop: