proxy: fix passing cancellable to async D-Bus operations

We must not cancel pacrunner_cancellable when the D-Bus proxy is
created. Instead, keep it around and use it later for the asynchronous
D-Bus operations.

This doesn't really matter at the moment, because the pacrunner manager
is only destroyed when NetworkManager is about to terminated. That is
the only time when we actually cancel the asynchronous request. Also,
at that time we no longer iterate the mainloop, so the pending requests
are never completed anyway.

(cherry picked from commit a08540d967)

src/nm-pacrunner-manager.c

@@ -330,7 +330,6 @@ pacrunner_proxy_cb (GObject *source, GAsyncResult *res, gpointer user_data)
 	priv = NM_PACRUNNER_MANAGER_GET_PRIVATE (self);
 
 	priv->pacrunner = proxy;
-	nm_clear_g_cancellable (&priv->pacrunner_cancellable);
 
 	g_signal_connect (priv->pacrunner, "notify::g-name-owner",
 	                  G_CALLBACK (name_owner_changed_cb), self);