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/frontend.c b/src/frontend.c
index 068e8d6..5f3d6cf 100644
--- a/src/frontend.c
+++ b/src/frontend.c
@@ -27,6 +27,7 @@
 #include <haproxy/chunk.h>
 #include <haproxy/frontend.h>
 #include <haproxy/sample.h>
+#include <haproxy/stream_interface.h>
 #include <haproxy/task.h>
 #include <haproxy/tools.h>
 #include <haproxy/time.h>
@@ -41,7 +42,6 @@
 #include <proto/http_ana.h>
 #include <proto/proxy.h>
 #include <proto/stream.h>
-#include <proto/stream_interface.h>
 
 /* Finish a stream accept() for a proxy (TCP or HTTP). It returns a negative
  * value in case of a critical failure which must cause the listener to be