Commit 
93821778def10ec1e69aa3ac10adee975dad4ff3 (udp: Fix rcv socket
locking) accidentally removed sk_drops increments for UDP IPV4
sockets.
This field can be used to detect incorrect sizing of socket receive
buffers.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
        if ((rc = sock_queue_rcv_skb(sk, skb)) < 0) {
                /* Note that an ENOMEM error is charged twice */
-               if (rc == -ENOMEM)
+               if (rc == -ENOMEM) {
                        UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_RCVBUFERRORS,
                                         is_udplite);
+                       atomic_inc(&sk->sk_drops);
+               }
                goto drop;
        }