neighbour: Do not perturb drop profiles when neigh_probe

Replace the kfree_skb() by consume_skb() to be drop monitor(dropwatch,
perf) friendly.
Signed-off-by: NYang Wei <yang.wei9@zte.com.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -1007,7 +1007,7 @@ static void neigh_probe(struct neighbour *neigh)
 	if (neigh->ops->solicit)
 		neigh->ops->solicit(neigh, skb);
 	atomic_inc(&neigh->probes);
-	kfree_skb(skb);
+	consume_skb(skb);
 }
 
 /* Called when a timer expires for a neighbour entry. */