igbvf: Fix trunk vlan

Changes to clean up the VLAN Rx path by Jiri Pirko broke trunk VLAN.
Trunk VLANs in a VF driver are those set using

"ip link set <pfdev> vf <n> <vlanid>"

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
CC: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>