[Babel-users] Specify router-id explicitly

[Juliusz Chroboczek]

>> Please do not make this option available in the OpenWRT config file.

> Unfortunately hnetd <> babeld communication occurs solely through
> configuration file (Fragment).

Ah merde.

> Therefore at least for those purposes it has to be there, if we were to
> use it.

Okay, then I'll make it into a config file option, and hope that people
aren't that stupid.

-- Juliusz