nixos/nsd: Fix indentation/coding style.

For Nix, we indent using two spaces, but in this module somehow 4 spaces
were snuck in. Other than that, remoteControl and ratelimit are just
nested attribute sets, so we don't need to make another submodule type
for no particular reason.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>