net/mlx5: Introduce and use mlx5_esw_is_manager_vport()

Currently esw_enable_vport() does vport check for zero to enable drop
counters regardless of execution on ECPF/PF.
While esw_disable_vport() considers such scenario.

To keep consistency across code for checking for manager_vport,
introduce and use mlx5_esw_is_manager_vport() to check if a specified
vport is eswitch manager vport or not.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Vu Pham <vuhuong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>