[Nix-dev] gw6c users: prepare to switch to gogoclient

[Mathijs Kwik]

Hi all,

The old gw6c ipv6 client hasn't been maintained for a few years.
It worked fine though, but it will break when the new stdenv merges.

The project continued, now named gogoclient.
I provided nixpkgs for it and now merged nixos support as well so it
should be trivial to switch.
It builds on the new stdenv, and forces secure password handling
compared to gw6c's seccurekeys trickerty that still needed a password
in configuration.nix.

I'm planning to remove gw6c completely in about a week time, to avoid confusion.
If you are still using gw6c please let me know if this is unacceptable to you.

Thanks,
Mathijs