networkmanager: Debounce unit change handler

firewalld_service's `changed` handler is called in bursts, for all the
internal systemd property changes like unit start times. These are not
interesting for firewall-client, and just lead to lots of duplicated
handler calls.

Remember the previous unit state, and short-circuit the handler
immediately if there is no interesting change.

pkg/networkmanager/firewall-client.js

@@ -204,20 +204,24 @@ function initFirewalldDbus() {
 
 firewalld_service.addEventListener('changed', () => {
  const installed = !!firewalld_service.exists;
+ const is_running = firewalld_service.state === 'running';
+
+ // we get lots of these events, for internal property changes; filter interesting changes
+ if (is_running === firewalld_service.prev_running && firewall.installed === installed)
+ return;
+ firewall.installed = installed;
+ firewalld_service.prev_running = is_running;
+
  debug("systemd service changed: exists", firewalld_service.exists, "state", firewalld_service.state,
  "firewall.enabled:", JSON.stringify(firewall.enabled));
 
  /* HACK: cockpit.dbus() remains dead for non-activatable names, so reinitialize it if the service gets enabled and started
  * See https://github.com/cockpit-project/cockpit/pull/9125 */
- if (!firewall.enabled && firewalld_service.state == 'running') {
+ if (!firewall.enabled && is_running) {
  debug("reinitializing D-Bus connection after unit got started");
  initFirewalldDbus();
  }
 
- if (firewall.installed == installed)
- return;
-
- firewall.installed = installed;
  firewall.dispatchEvent('changed');
 });