IIRC, we have ``vm.deactivate_nic() + vm.del_nic()`` and ``vm.add_nic() + vm.activate_nic()`` interface.  The only thing missing is the libvirt_vm activate/deactivate methods.  Since 'modify_network' may be a common operation, how about move this code into ``libvirt_vm.VM.activate/deactivate_nic()``?