nixos/clatd: allow AF_UNIX communication

This is needed since clatd will use networkctl to attempt to obtain the
PLAT prefix, and networkctl uses UNIX domain sockets to communicate with
the systemd-networkd daemon over DBus.

nixos/modules/services/networking/clatd.nix

@@ -75,6 +75,7 @@ in
           "AF_INET"
           "AF_INET6"
           "AF_NETLINK"
+          "AF_UNIX"
         ];
         RestrictNamespaces = true;
         RestrictRealtime = true;