vxlan: handle skb_clone failure

If skb_clone fails if out of memory then just skip the fanout.

Problem was introduced in 3.10 with:
  commit 6681712d
  Author: David Stevens <dlstevens@us.ibm.com>
  Date:   Fri Mar 15 04:35:51 2013 +0000

    vxlan: generalize forwarding tables
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -1161,9 +1161,11 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
 		struct sk_buff *skb1;
 
 		skb1 = skb_clone(skb, GFP_ATOMIC);
-		rc1 = vxlan_xmit_one(skb1, dev, rdst, did_rsc);
-		if (rc == NETDEV_TX_OK)
-			rc = rc1;
+		if (skb1) {
+			rc1 = vxlan_xmit_one(skb1, dev, rdst, did_rsc);
+			if (rc == NETDEV_TX_OK)
+				rc = rc1;
+		}
 	}
 
 	rc1 = vxlan_xmit_one(skb, dev, rdst0, did_rsc);