net/mlx5: E-Switch, Use getter to access all vport array

Some functions issue vport commands and access vport array using
vport_index/vport_num interchangeably which is OK for VFs vports.
However, this creates potential bug if those vports are not VFs
(E.g, uplink, sf) where their vport_index don't equal to vport_num.

Prepare code to access mlx5_vport structure using a getter function.

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