i40e: report VF MAC addresses correctly

If the user does not assign a VF MAC address, then just report it as
zero.  Attempting to guess the correct primary MAC address of the VF is a
futile and heartbreaking endeavour.

Change-Id: I2673577a160afb6fc55094c890467b44e60c7584
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>