Let resolvconf 'restart' the nscd service instead of 'reload'ing it.

Sometimes nscd starts up before a /etc/resolv.conf file has been written, and
apparently triggering a cache flush (reload) is not good enough to make it
recover from that problem. To remedy the issue, we restart the service instead.
See <https://github.com/NixOS/nixos/issues/34> for further details.