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

This is in order to keep things consistent.
diff --git a/include/proto/stream.h b/include/proto/stream.h
index c73ad20..ba2c943 100644
--- a/include/proto/stream.h
+++ b/include/proto/stream.h
@@ -41,7 +41,7 @@
 /* perform minimal intializations, report 0 in case of error, 1 if OK. */
 int init_stream();
 
-/* kill a stream and set the termination flags to <why> (one of SN_ERR_*) */
+/* kill a stream and set the termination flags to <why> (one of SF_ERR_*) */
 void stream_shutdown(struct stream *stream, int why);
 
 void stream_process_counters(struct stream *s);