ppp: fix cancelling timeout when pppd process exits

Otherwise, we get pppd_timed_out() later, which will
emit a DEAD state change at unexpected times.

src/ppp/nm-ppp-manager.c

@@ -643,6 +643,7 @@ ppp_watch_cb (GPid pid, int status, gpointer user_data)
 
 	priv->pid = 0;
 	priv->ppp_watch_id = 0;
+	_ppp_cleanup (manager);
 	g_signal_emit (manager, signals[STATE_CHANGED], 0, (guint) NM_PPP_STATUS_DEAD);
 }