net/mlx5e: Abstract MQPRIO params

Abstract the MQPRIO params into a struct.
Use a getter for DCB mode num_tcs.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>