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.