hv_netvsc: Fix VF register on vlan devices

Added a condition to avoid vlan devices with same MAC registering
as VF.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>