How to determine identity of obscure `nic:br-` devices in powertop?
These are ethernet bridge devices, and you can investigate them with the /sbin/bridge or the older /sbin/brctl utilities. You can bring them down with the traditional ifconfig <dev> down command.
In this case it looks like they are created by Docker. I recently discovered that these devices seem to persist and defy power management even if you're not immediately running Docker.