net/hyperv: Add support for vlan trunking from guests

With this feature, a Linux guest can now configure multiple vlans through
a single synthetic NIC on Win8 Hyper-V host.

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>