In order to properly restore the original state of an SRIOV VF when
we're finished with it, we need to save the MAC address of the VF
itself (not just the admin MAC address for the VF that is stored in
the PF). But that can only be done when the VF is still bound to the
host's netdev driver, and we have always done the saving of device
config after the VF is already bound to vfio-pci. This patch prepares
us for adding a save of the VF's MAC by calling the function that
saves netconfig earlier in the device preparation, before we've
unbound it from the host netdev driver.