vxlan: using pskb_may_pull as early as possible

pskb_may_pull should be used to check if skb->data has enough space,
skb->len can not ensure that.

Cc: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -1437,9 +1437,6 @@ static int neigh_reduce(struct net_device *dev, struct sk_buff *skb)
 	if (!in6_dev)
 		goto out;
 
-	if (!pskb_may_pull(skb, skb->len))
-		goto out;
-
 	iphdr = ipv6_hdr(skb);
 	saddr = &iphdr->saddr;
 	daddr = &iphdr->daddr;
@@ -1880,7 +1877,8 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
 			return arp_reduce(dev, skb);
 #if IS_ENABLED(CONFIG_IPV6)
 		else if (ntohs(eth->h_proto) == ETH_P_IPV6 &&
-			 skb->len >= sizeof(struct ipv6hdr) + sizeof(struct nd_msg) &&
+			 pskb_may_pull(skb, sizeof(struct ipv6hdr)
+				       + sizeof(struct nd_msg)) &&
 			 ipv6_hdr(skb)->nexthdr == IPPROTO_ICMPV6) {
 				struct nd_msg *msg;