net/mlx4_en: use __netdev_tx_sent_queue()

doorbell only depends on xmit_more and netif_tx_queue_stopped()

Using __netdev_tx_sent_queue() avoids messing with BQL stop flag,
and is more generic.

This patch increases performance on GSO workload by keeping
doorbells to the minimum required.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>