Backward compatibility hack for ‘networking.nat.internalIPs’

modules/services/networking/nat.nix

@@ -34,6 +34,9 @@ in
           coming from these networks and destined for the external
           interface will be rewritten.
         '';
+      # Backward compatibility: this used to be a single range instead
+      # of a list.
+      apply = x: if isList x then x else [x];
     };
 
     networking.nat.externalInterface = mkOption {