REORG: rename cs_utils.h to sc_strm.h

This file contains all the stream-connector functions that are specific
to application layers of type stream. So let's name it accordingly so
that it's easier to figure what's located there.

The alphabetical ordering of include files was preserved.
diff --git a/src/backend.c b/src/backend.c
index 7b88097..ea5f332 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -28,7 +28,6 @@
 #include <haproxy/channel.h>
 #include <haproxy/check.h>
 #include <haproxy/conn_stream.h>
-#include <haproxy/cs_utils.h>
 #include <haproxy/frontend.h>
 #include <haproxy/global.h>
 #include <haproxy/hash.h>
@@ -50,6 +49,7 @@
 #include <haproxy/proxy.h>
 #include <haproxy/queue.h>
 #include <haproxy/sample.h>
+#include <haproxy/sc_strm.h>
 #include <haproxy/server.h>
 #include <haproxy/session.h>
 #include <haproxy/ssl_sock.h>