netpoll: fix the skb check in pkt_is_ns

[ Not applicable upstream commit, the code here has been removed
  upstream. ]

Neighbor Solicitation is ipv6 protocol, so we should check
skb->protocol with ETH_P_IPV6
Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Cc: WANG Cong <amwang@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/core/netpoll.c

@@ -740,7 +740,7 @@ static bool pkt_is_ns(struct sk_buff *skb)
 	struct nd_msg *msg;
 	struct ipv6hdr *hdr;
 
-	if (skb->protocol != htons(ETH_P_ARP))
+	if (skb->protocol != htons(ETH_P_IPV6))
 		return false;
 	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr) + sizeof(struct nd_msg)))
 		return false;