mlx4_en: Consider napi_get_frags() failure.

If failed to get skb frags using napi_get_frags(),
the packet is dropped.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/mlx4/en_rx.c b/drivers/net/mlx4/en_rx.c
index c4aad7f..570f250 100644
--- a/drivers/net/mlx4/en_rx.c
+++ b/drivers/net/mlx4/en_rx.c
@@ -591,6 +591,8 @@
 				 * - not an IP fragment */
 				if (dev->features & NETIF_F_GRO) {
 					struct sk_buff *gro_skb = napi_get_frags(&cq->napi);
+					if (!gro_skb)
+						goto next;
 
 					nr = mlx4_en_complete_rx_desc(
 						priv, rx_desc,