nfp: support 802.1ad VLAN assingment to VF

The NFP driver already supports assignment of 802.1Q VLANs to VFs

e.g.
 # ip link set $DEV vf $VF_NUM vlan $VLAN_ID [proto 802.1Q]

This patch enhances the NFP driver to also allow assingment of
802.1ad VLANs to VFs.

e.g.
 # ip link set $DEV vf $VF_NUM vlan $VLAN_ID proto 802.1ad

Signed-off-by: Bin Chen <bin.chen@corigine.com>
Signed-off-by: Baowen Zheng <baowen.zheng@corigine.com>
Signed-off-by: Yinjun Zhang <yunjin.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>