net/mlx5e: Improve MQPRIO resiliency

* Add netdev->tc_to_txq rollback in case of failure in
  mlx5e_update_netdev_queues().
* Fix broken transition between the two modes:
  MQPRIO DCB mode with tc==8, and MQPRIO channel mode.
* Disable MQPRIO channel mode if re-attaching with a different number
  of channels.
* Improve code sharing.

Fixes: ec60c458

 ("net/mlx5e: Support MQPRIO channel mode")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>