a work for lxc monitor network interface

[Libo Chen <clbchenlibo.chen-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

Hello LXC experts,

	lxc tool can set network interface by config, but it is static.
In some scene, the network interface will be dynamic created on the host
and need be shared to container, but it is not suitable to do by hand,
so lxc can not work for it.

	I also know lxc_user_nic() can only do a part of work, but we have
two more work:
1. grasp the netlink/uevent message about network interface online
2. config interface attached to container ip address .

so it can not fully meet my requirements.

	I want there is a monitor can work for network interface hotplug.

1. read config form config file, it describe monitor which network interface
   and what's the network configuration
2. grasp the netlink/uevent message about network interface online on the host
3. create veth pair, put veth attach to container and bridge
4. config the veth attached to container ipaddr

			
         	          netlink  create veth pair
monitor ---> read config  -------> veth0 attach to container --> config ipaddr
				   veth1 attach to bridge

monitor may be the lxc-start or a child forked by lxc-start.


 Is this reasonable?  If so, I'd like to do it.