net/mlx5: Lag, correct get the port select mode str

mode & mode_flags is updated at the end of mlx5_activate_lag which
may not reflect the actual mode as shown in below logic:
    mlx5_activate_lag(struct mlx5_lag *ldev,
    |-- unsigned long flags = 0;
    |-- err = mlx5_lag_set_flags(ldev, mode, tracker, shared_fdb, &flags);
    |-- err = mlx5_create_lag(ldev, tracker, mode, flags);
              |-- mlx5_get_str_port_sel_mode(ldev);
    |-- ldev->mode = mode;
    |-- ldev->mode_flags = flags;
Use mode & flag as parameters to get port select mode info.

Fixes: 94db3317 ("net/mlx5: Support multiport eswitch mode")
Signed-off-by: Liu, Changcheng <jerrliu@nvidia.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>