As I explained to @yangdongsheng face to face, self.get_structure() like this:
```
{ "br0"      :   ["eth0", "eth1"],
   "virtbr0" :   ["eth2", "eth3"]}
```
So, self.get_structure().values is:
[["eth0", "eth1"], ["eth2", "eth3"]].
But I want ["eth0", "eth1", "eth2", "eth3"], so I use
`list(set(["eth0", "eth1"]+["eth2", "eth3"]))`.
So I think here needs no modification..:)