[upnpcontrol] discover child devices (#18721)

Signed-off-by: Andrew Fiddian-Green <software@whitebear.ch>

bundles/org.openhab.binding.upnpcontrol/src/main/java/org/openhab/binding/upnpcontrol/internal/discovery/UpnpControlDiscoveryParticipant.java

@@ -95,4 +95,9 @@ public class UpnpControlDiscoveryParticipant implements UpnpDiscoveryParticipant
         }
         return result;
     }
+
+    @Override
+    public boolean notifyChildDevices() {
+        return true;
+    }
 }