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: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>