ax25: In ax25_rebuild_header add missing kfree_skb

In the unlikely (impossible?) event that we attempt to transmit
an ax25 packet over a non-ax25 device free the skb so we don't
leak it.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-hams@vger.kernel.org
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ax25/ax25_ip.c

@@ -129,6 +129,7 @@ int ax25_rebuild_header(struct sk_buff *skb)
 		dev = skb->dev;
 
 	if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL) {
+		kfree_skb(skb);
 		goto put;
 	}