net/iavf: fix VLAN tag extraction handling

net/iavf: fix VLAN tag extraction handling

The new VIRTCHNL_VF_OFFLOAD_VLAN_V2 capability added support that allows
the PF to set the location of the RX VLAN tag for stripping offloads.

So the VF needs to extract the VLAN tag according to the location flags.

Fixes: 1c301e8c3cff ("net/iavf: support new VLAN capabilities")
Cc: stable@dpdk.org
Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Signed-off-by: Leyi Rong <leyi.rong@intel.com>
Tested-by: Wei Xie <weix.xie@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>