tpacket_snd() can change and kfree an skb after dev_queue_xmit(),
which is illegal.

With debugging by: Stephen Hemminger <shemminger@vyatta.com>
Reported-by: NMichael Breuer <mbreuer@majjas.com>
With help from: David S. Miller <davem@davemloft.net>
Signed-off-by: NJarek Poplawski <jarkao2@gmail.com>
Tested-by: Michael Breuer<mbreuer@majjas.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>