[MINOR] stats_dump_sess_to_buffer: use buffer_feed_chunk()

same as previous patch for this function.
diff --git a/include/proto/dumpstats.h b/include/proto/dumpstats.h
index 4dd9e34..990c620 100644
--- a/include/proto/dumpstats.h
+++ b/include/proto/dumpstats.h
@@ -50,7 +50,7 @@
 void stats_dump_raw_to_buffer(struct session *s, struct buffer *req);
 int stats_dump_http(struct session *s, struct buffer *rep, struct uri_auth *uri);
 int stats_dump_proxy(struct session *s, struct proxy *px, struct uri_auth *uri);
-void stats_dump_sess_to_buffer(struct session *s, struct buffer *rep);
+int stats_dump_sess_to_buffer(struct session *s, struct buffer *rep);
 int stats_dump_errors_to_buffer(struct session *s, struct buffer *rep);