net/mlx5e: Add TXQ set max rate support

Implement set_maxrate ndo.
Use the rate index from the hardware table to attach to channel SQ/TXQ.
In case of failure to configure new rate, the queue remains with
unlimited rate.

We save the configuration on priv structure and apply it each time
Send Queues are being reinitialized (after open/close) operations.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>