iavf: Fix handling of vlan strip virtual channel messages

Modify netdev->features for vlan stripping based on virtual
channel messages received from the PF. Change is needed
to synchronize vlan strip status between PF sysfs and iavf ethtool.

Fixes: 5951a2b9 ("iavf: Fix VLAN feature flags after VFR")
Signed-off-by: Norbert Ciosek <norbertx.ciosek@intel.com>
Signed-off-by: Michal Maloszewski <michal.maloszewski@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>