fix: close leaked resource handles (#2040)

src/activities/network/CalibreConnectActivity.cpp

@@ -52,6 +52,8 @@ void CalibreConnectActivity::onEnter() {
 void CalibreConnectActivity::onExit() {
   Activity::onExit();
 
+  MDNS.end();
+
   if (WiFi.getMode() != WIFI_MODE_NULL) {
     WiFi.disconnect(false);
     delay(30);
@@ -72,6 +74,7 @@ void CalibreConnectActivity::startWebServer() {
   state = CalibreConnectState::SERVER_STARTING;
   requestUpdate();
 
+  MDNS.end();
   if (MDNS.begin(HOSTNAME)) {
     // mDNS is optional for the Calibre plugin but still helpful for users.
     LOG_DBG("CAL", "mDNS started: http://%s.local/", HOSTNAME);