net/mlx5e: Set SQ max rate on mlx5e_open_txqsq rather on open_channel

Instead of iterating over the channel SQs to set their max rate, do it
on SQ creation per TXQ SQ.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>