ieee802154: 6lowpan: trivial checks at first

This patch moves some trivial checks at first before calling
skb_share_check which could do some memcpy if the buffer is shared.
Reviewed-by: NStefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: NAlexander Aring <alex.aring@gmail.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/ieee802154/6lowpan/rx.c

@@ -63,7 +63,8 @@ static int lowpan_rcv(struct sk_buff *skb, struct net_device *wdev,
 	struct net_device *ldev;
 	int ret;
 
-	if (wdev->type != ARPHRD_IEEE802154)
+	if (wdev->type != ARPHRD_IEEE802154 ||
+	    skb->pkt_type == PACKET_OTHERHOST)
 		goto drop;
 
 	ldev = wdev->ieee802154_ptr->lowpan_dev;
@@ -74,9 +75,6 @@ static int lowpan_rcv(struct sk_buff *skb, struct net_device *wdev,
 	if (!skb)
 		goto drop;
 
-	if (skb->pkt_type == PACKET_OTHERHOST)
-		goto drop_skb;
-
 	if (ieee802154_hdr_peek_addrs(skb, &hdr) < 0)
 		goto drop_skb;