Add missing 'type', 'defaultText' and 'literalExample' in module definitions

- add missing types in module definitions
- add missing 'defaultText' in module definitions
- wrap example with 'literalExample' where necessary in module definitions

nixos/modules/services/networking/firewall.nix

@@ -421,8 +421,9 @@ in
     };
 
     networking.firewall.extraPackages = mkOption {
+      type = types.listOf types.package;
       default = [ ];
-      example = [ pkgs.ipset ];
+      example = literalExample "[ pkgs.ipset ]";
       description =
         ''
           Additional packages to be included in the environment of the system