i40e: Retain MAC filters when changing port VLAN

We were already taking care to retain the MAC filter list when deleting a
port VLAN.  Take some additional care to retain the MAC filter list when
changing a port VLAN.

Change-ID: Iacf9599ea24ecb4dca8e419aacaf4b58ca361a9c
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>