net/mlx5: Introduce access functions to modify/query vport state

In preparation for SR-IOV we add here an API to enable each e-switch
manager (PF) to configure its VFs link states in e-switch

preparation for ethernet sriov.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>