Bluetooth: 6lowpan: Avoid memory leak if memory allocation fails

If skb_unshare() returns NULL, then we leak the original skb.
Solution is to use temp variable to hold the new skb.
Signed-off-by: NJukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: NJohan Hedberg <johan.hedberg@intel.com>

net/bluetooth/6lowpan.c

@@ -589,13 +589,17 @@ static netdev_tx_t bt_xmit(struct sk_buff *skb, struct net_device *netdev)
 	int err = 0;
 	bdaddr_t addr;
 	u8 addr_type;
+	struct sk_buff *tmpskb;
 
 	/* We must take a copy of the skb before we modify/replace the ipv6
 	 * header as the header could be used elsewhere
 	 */
-	skb = skb_unshare(skb, GFP_ATOMIC);
-	if (!skb)
+	tmpskb = skb_unshare(skb, GFP_ATOMIC);
+	if (!tmpskb) {
+		kfree_skb(skb);
 		return NET_XMIT_DROP;
+	}
+	skb = tmpskb;
 
 	/* Return values from setup_header()
 	 *  <0 - error, packet is dropped