pupnp: unregister libupnp client handle when clearing IGDs

The PUPnP::clearIgds function is called when the UPnP context is
stopped. We don't want to keep receiving and processing IGD events after
that point, so we need to unregister our libupnp "client handle".

GitLab: #29
Change-Id: I017e6ec8aea1423d63381c9e5b3952cff7dfeb2e
diff --git a/src/upnp/protocol/pupnp/pupnp.h b/src/upnp/protocol/pupnp/pupnp.h
index 03086dd..5bba6dc 100644
--- a/src/upnp/protocol/pupnp/pupnp.h
+++ b/src/upnp/protocol/pupnp/pupnp.h
@@ -124,6 +124,9 @@
     // Register the client
     void registerClient();
 
+    // Unregister the client
+    void unregisterClient();
+
     // Start search for UPNP devices
     void searchForDevices();