net: Convert qdev_prop_vlan to peer with hub

net: Convert qdev_prop_vlan to peer with hub

Instead of using VLANState use net/hub.h to support the vlan qdev
property.  The vlan qdev property becomes an alias for the peer qdev
property but is represented as a VLAN ID number.  When a VLAN ID is
selected the device will really peer with a hub port.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>