this makes it so if we restart the wireguard connection, the services
themeselves _also_ restart. that should avoid leaving any of them in an
orphaned namespace
- shorter.
- congruent with `nixos-rebuild .` choosing what to build based on `hostname`.
- more widely used within other nix repos i've seen.
- more accurate in the case that i migrate a host to a different
machine (which i plan to do with servo).