Add ndo_set_tx_maxrate support.

To support per tx queue maxrate limit, we use the update-qp firmware
command to do run-time rate setting for the qp that serves this tx ring.
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>