REORG: include: move stream_interface.h to haproxy/stream_interface{,-t}.h

Almost no changes, removed stdlib and added buf-t and connection-t to
the types to avoid a warning.
diff --git a/src/ring.c b/src/ring.c
index cdf9185..437ee39 100644
--- a/src/ring.c
+++ b/src/ring.c
@@ -25,7 +25,7 @@
 #include <haproxy/cli.h>
 #include <haproxy/thread.h>
 #include <haproxy/ring.h>
-#include <proto/stream_interface.h>
+#include <haproxy/stream_interface.h>
 
 /* Creates and returns a ring buffer of size <size> bytes. Returns NULL on
  * allocation failure.