Use the default timeout on DBus calls

We were using a very short timeout (3 ms) on one of the dbus calls.

libgupnp/gupnp-network-manager.c

@@ -763,7 +763,7 @@ gupnp_network_manager_is_available (GMainContext *main_context)
                                              g_variant_new ("(s)",
                                                             DBUS_SERVICE_NM),
                                              G_DBUS_CALL_FLAGS_NONE,
-                                             3,
+                                             -1,
                                              NULL,
                                              &error);
         if (error != NULL) {