mlx4_en: Cancel port_up check in transmit function

When closing the port, we stop all transmit queues under the transmit
lock. It ensures that we will not attempt to transmit new packets after
the physical port was closed.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>