nixos/avahi: move nss database configuration into avahi module

nixos/modules/config/nsswitch.nix

@@ -9,15 +9,12 @@ let
   # only with nscd up and running we can load NSS modules that are not integrated in NSS
   canLoadExternalModules = config.services.nscd.enable;
   # XXX Move these to their respective modules
-  nssmdns = canLoadExternalModules && config.services.avahi.nssmdns;
   nsswins = canLoadExternalModules && config.services.samba.nsswins;
 
   hostArray = mkMerge [
     (mkBefore [ "files" ])
-    (mkIf nssmdns [ "mdns_minimal [NOTFOUND=return]" ])
     (mkIf nsswins [ "wins" ])
     (mkAfter [ "dns" ])
-    (mkIf nssmdns (mkOrder 1501 [ "mdns" ])) # 1501 to ensure it's after dns
   ];
 
 in {

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

@@ -238,6 +238,10 @@ in
     users.groups.avahi = {};
 
     system.nssModules = optional cfg.nssmdns pkgs.nssmdns;
+    system.nssDatabases.hosts = optionals cfg.nssmdns (mkMerge [
+      [ "mdns_minimal [NOTFOUND=return]" ]
+      (mkOrder 1501 [ "mdns" ]) # 1501 to ensure it's after dns
+    ]);
 
     environment.systemPackages = [ pkgs.avahi ];