message: remove 'leave' operation to avoid change existing WPAN status
diff: @@ -321,8 +321,6 @@ std::string WpanService::HandleAvailableNetworkRequest()
  int ret = ot::Dbus::kWpantundStatus_Ok;
  wpanController.SetInterfaceName(mIfName);
  - VerifyOrExit(wpanController.Leave() == ot::Dbus::kWpantundStatus_Ok,
  - ret = ot::Dbus::kWpantundStatus_LeaveFailed);
  VerifyOrExit(wpanController.Scan() == ot::Dbus::kWpantundStatus_Ok,
  ret = ot::Dbus::kWpantundStatus_ScanFailed);
  mNetworksCount = wpanController.GetScanNetworksInfoCount();
  