Stop using the special-case vlan code in net.c.  Instead use the hub net
client to implement the vlan feature.  The next patch will remove vlan
code from net.c completely.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NZhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>