nfp: use the new __netdev_tx_sent_queue() BQL optimisation

__netdev_tx_sent_queue() was added in commit e59020abf0f
("net: bql: add __netdev_tx_sent_queue()") and allows for
better GSO performance.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>