nixos/avahi: rename remaining config options

services.avahi.nssmdns got split into services.avahi.nssmdns{4,6},
nothing should access the old alias anymore so there's no eval warnings.

Reported in https://github.com/NixOS/nixpkgs/pull/258424#issuecomment-1849428869

nixos/modules/services/networking/avahi-daemon.nix

···
 
     users.groups.avahi = { };
 
-    system.nssModules = optional cfg.nssmdns pkgs.nssmdns;
+    system.nssModules = optional (cfg.nssmdns4 || cfg.nssmdns6) pkgs.nssmdns;
     system.nssDatabases.hosts = let
       mdnsMinimal = if (cfg.nssmdns4 && cfg.nssmdns6) then
         "mdns_minimal"

nixos/tests/avahi.nix

···
     cfg = { ... }: {
       services.avahi = {
         enable = true;
-        nssmdns = true;
+        nssmdns4 = true;
         publish.addresses = true;
         publish.domain = true;
         publish.enable = true;

nixos/tests/guix/publish.nix

···
       # substitute server which requires Avahi.
       services.avahi = {
         enable = true;
-        nssmdns = true;
+        nssmdns4 = true;
         publish = {
           enable = true;
           userServices = true;

pkgs/applications/misc/keylight-controller-mschneider82/default.nix

···
     longDescription = ''
       Requires having:
       * Elgato's Keylight paired to local wifi network.
-      * Service avahi with nssmdns enabled.
+      * Service avahi with nssmdns4 enabled.
     '';
     license = licenses.mit;
     homepage = "https://github.com/mschneider82/keylight-control";

pkgs/misc/drivers/epson-escpr/default.nix

···
       hostname resolvable:
         services.avahi = {
           enable = true;
-          nssmdns = true;
+          nssmdns4 = true;
         };'';
     license = licenses.gpl3Plus;
     maintainers = with maintainers; [ artuuge ];