MINOR: stconn/channel: Move CF_READ_DONTWAIT into the SC and rename it

The channel flag CF_READ_DONTWAIT is renamed to SC_FL_RCV_ONCE and moved
into the stream-connector.
diff --git a/src/http_client.c b/src/http_client.c
index a30a941..c146bd2 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -1071,9 +1071,8 @@
 		s->scb->dst = addr;
 	}
 
-	s->scb->flags |= SC_FL_NOLINGER;
+	s->scb->flags |= (SC_FL_RCV_ONCE|SC_FL_NOLINGER);
 	s->flags |= SF_ASSIGNED;
-	s->res.flags |= CF_READ_DONTWAIT;
 
 	/* applet is waiting for data */
 	applet_need_more_data(appctx);