nixos/acme: make address families in systemd service less restrictive

This change is to support LEGO's capability to spawn an external process that
solves the DNS-01 challenge. In particular, this enables a setup where LEGO
runs a shell script that uses nsd-control to add an appropriate zone to a
local NSD instance.

(cherry picked from commit d9bf91700e)

nixos/modules/security/acme/default.nix

@@ -87,6 +87,8 @@ let
     RestrictAddressFamilies = [
       "AF_INET"
       "AF_INET6"
+      "AF_UNIX"
+      "AF_NETLINK"
     ];
     RestrictNamespaces = true;
     RestrictRealtime = true;