net: fix memory leak on oom with zerocopy

If orphan flags fails, we don't free the skb
on receive, which leaks the skb memory.

Return value was also wrong: netif_receive_skb
is supposed to return NET_RX_DROP, not ENOMEM.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -3322,7 +3322,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
 
 	if (pt_prev) {
 		if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
-			ret = -ENOMEM;
+			goto drop;
 		else
 			ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
 	} else {