VFs rely on config BAR for getting the MAC address, although a
random one is created a valid address is not found.
A PF port has a fixed MAC which is currently acquired using the NSPU
interface. Some NFP firmwares require the MAC being writing back
to the config BAR for doing proper MAC filtering.
Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>