6LoWPAN: use kfree_skb() instead of kfree()

Use kfree_skb() to free sbk_buffs.

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ieee802154/6lowpan.c

···
 							sizeof(hdr));
 	return lowpan_skb_deliver(skb, &hdr);
 drop:
-	kfree(skb);
+	kfree_skb(skb);
 	return -EINVAL;
 }