Fixes #6444 - add support for virtual NICs

fair point. So are we envisaging something like this?
```
parent - bond0 (sti type: bond)
   -> child - eth0 (sti type: interface)
   -> child - eth1 (sti type: interface)

parent eth0.0 (sti type: interface)
   -> child - eth0 (sti type: interface)
```