ntb_netdev: remove tx timeout

There is a race between disabling and enabling the tx queue, resulting
in tx timeouts.  Since all the tx timeout does is re-enable the tx
queue, simple remove the start/stop of the queue and the tx timeout
routine.

Signed-off-by: Jon Mason <jon.mason@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>