net: use skb_clone to avoid alloc_pages failure.

1. new skb only need dst and ip address(v4 or v6).
2. skb_copy may need high order pages, which is very rare on long running server.
Signed-off-by: Junwei Zhang <linggao.zjw@alibaba-inc.com>
Signed-off-by: Martin Zhang <martinbj2008@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -857,7 +857,7 @@ static void neigh_probe(struct neighbour *neigh)
 	struct sk_buff *skb = skb_peek_tail(&neigh->arp_queue);
 	/* keep skb alive even if arp_queue overflows */
 	if (skb)
-		skb = skb_copy(skb, GFP_ATOMIC);
+		skb = skb_clone(skb, GFP_ATOMIC);
 	write_unlock(&neigh->lock);
 	neigh->ops->solicit(neigh, skb);
 	atomic_inc(&neigh->probes);