MINOR: conn_stream: modify cs_shut{r,w} API to pass the desired mode

Now we can specify how we want to shutdown (drain vs reset, and normal
vs silent), and this propagates to the mux then the transport layer.
diff --git a/src/checks.c b/src/checks.c
index 57468e0..ee0458d 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -1344,7 +1344,7 @@
 	 * drain pending data.
 	 */
 	__cs_stop_both(cs);
-	cs_shutw(cs);
+	cs_shutw(cs, CS_SHW_NORMAL);
 
 	/* OK, let's not stay here forever */
 	if (check->result == CHK_RES_FAILED)