net/mlx5e: Handle errors of netdev_set_num_tc()

Add handling for failures in netdev_set_num_tc().
Let mlx5e_netdev_set_tcs return an int.

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