i40e/i40evf: support for VF VLAN tag stripping control

This patch gives VF capability to control VLAN tag stripping via
ethtool. As rx-vlan-offload was fixed before, now the VF is able to
change it using "ethtool --offload <IF> rxvlan on/off" settings.

Signed-off-by: Mariusz Stachura <mariusz.stachura@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>