net/mlx5e: E-Switch, Allow get vport api if esw exists

We could have an esw manager device which is not a vport group manager.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>