avahi: rename nssmdns to its new name

enables both ipv4 and ipv6

modules/network/avahi.nix

@@ -3,6 +3,7 @@
 {
   services.avahi = {
     enable = true;
-    nssmdns = true;
+    nssmdns4 = true;
+    nssmdns6 = true;
   };
 }