[bug] Re-ordering templates in device add view

It is not possible to re-order template in add view of DeviceAdmin. Even after dragging, the order of templates is not changed. 

![](https://user-images.githubusercontent.com/841044/114784634-2094f480-9d41-11eb-9230-4145c88caa10.gif)

Originally found here: https://github.com/openwisp/openwisp-controller/pull/428#pullrequestreview-635840867