These devices don't have unique MAC addresses with OpenWrt/LEDE at the moment
(see #993).

Fixes #961

* use tabs instead of spaces
* use jsonfilter for speed

propose to make uci commit more specific to minimize unwanted changes in other temporary written config files like wireless ssid (in some offline changers)

Tested build on a minimal Ubuntu 16.04 container image without wget.

Tested-by: Jannis Pinter <jannis@pinterjann.is>