nixos/avahi: add debug option

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

@@ -276,6 +276,8 @@ in
         Extra config to append to avahi-daemon.conf.
       '';
     };
+
+    debug = lib.mkEnableOption "debug logging";
   };
 
   config = lib.mkIf cfg.enable {
@@ -356,7 +358,7 @@ in
         NotifyAccess = "main";
         BusName = "org.freedesktop.Avahi";
         Type = "dbus";
-        ExecStart = "${cfg.package}/sbin/avahi-daemon --syslog -f ${avahiDaemonConf}";
+        ExecStart = "${cfg.package}/sbin/avahi-daemon --syslog -f ${avahiDaemonConf} ${lib.optionalString cfg.debug "--debug"}";
         ConfigurationDirectory = "avahi/services";
 
         # Hardening

nixos/tests/avahi.nix

@@ -24,6 +24,7 @@
             publish.userServices = true;
             publish.workstation = true;
             extraServiceFiles.ssh = "${pkgs.avahi}/etc/avahi/services/ssh.service";
+            debug = true;
           };
         }
         // pkgs.lib.optionalAttrs networkd {