Another step in moving the vlan feature out of net core.  Users only
deal with NetClientState and therefore qemu_del_vlan_client() should be
named qemu_del_net_client().
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>