Phonet: dropped datagrams accounting

The per-socket drop count is visible via /proc/net/phonet.
Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/phonet/datagram.c

@@ -159,8 +159,11 @@ out_nofree:
 static int pn_backlog_rcv(struct sock *sk, struct sk_buff *skb)
 {
 	int err = sock_queue_rcv_skb(sk, skb);
-	if (err < 0)
+	if (err < 0) {
 		kfree_skb(skb);
+		if (err == -ENOMEM)
+			atomic_inc(&sk->sk_drops);
+	}
 	return err ? NET_RX_DROP : NET_RX_SUCCESS;
 }