REORG/MEDIUM: stream: rename stream flags from SN_* to SF_*

This is in order to keep things consistent.
diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index f96d81c..801e4d8 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -371,14 +371,14 @@
 static inline int si_connect(struct stream_interface *si)
 {
 	struct connection *conn = objt_conn(si->end);
-	int ret = SN_ERR_NONE;
+	int ret = SF_ERR_NONE;
 
 	if (unlikely(!conn || !conn->ctrl || !conn->ctrl->connect))
-		return SN_ERR_INTERNAL;
+		return SF_ERR_INTERNAL;
 
 	if (!conn_ctrl_ready(conn) || !conn_xprt_ready(conn)) {
 		ret = conn->ctrl->connect(conn, !channel_is_empty(si_oc(si)), 0);
-		if (ret != SN_ERR_NONE)
+		if (ret != SF_ERR_NONE)
 			return ret;
 
 		/* we need to be notified about connection establishment */