mlx4_en: Fix BQL reset TX queue call point

Fix issue in Mellanox driver related to BQL.  netdev_tx_reset_queue
was not being called in certain situations where the device was
being start and stopped.  Moved netdev_tx_reset_queue from the reset
device path to mlx4_en_free_tx_buf which is where the rings are
cleaned in a reset (specifically from device being stopped).

Signed-off-by: Tom Herbert <therbert@google.com>
Acked-By: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>