ieee802154: dont leak skbs in ieee802154_fake_xmit()

ieee802154_fake_xmit() should free skbs since it returns NETDEV_TX_OK

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>