net/mlx5_core: Break down the vport mac address query function

Introduce a new function called mlx5_query_nic_vport_context().
This function gets all the NIC vport attributes from the device.

The MAC address is just one of the NIC vport attributes, so
mlx5_query_nic_vport_mac_address() is now just a wrapper function
above mlx5_query_nic_vport_context().

More NIC vport attributes will be used in following commits.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>