add debug logging

src/core/ngx_output_chain.c

diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index cc635c9..554fe1b 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -444,8 +444,9 @@
 
         size += ngx_buf_size(in->buf);
 
-        ngx_log_debug1(NGX_LOG_DEBUG_CORE, ctx->connection->log, 0,
-                       "chain writer buf size: %uO", ngx_buf_size(in->buf));
+        ngx_log_debug2(NGX_LOG_DEBUG_CORE, ctx->connection->log, 0,
+                       "chain writer buf fl:%d s:%uO",
+                       in->buf->flush, ngx_buf_size(in->buf));
 
         cl = ngx_alloc_chain_link(ctx->pool);
         if (cl == NULL) {