Use the netdevice transmit lock via netif_tx_lock rather than putting
lock in device specific code and using lockless transmit.  The code is
cleaner using netif_tx_lock, and the performance is same.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NJeff Garzik <jeff@garzik.org>