Add metadata refcount debugging
diff --git a/src/core/transport/transport.c b/src/core/transport/transport.c
index fe56594..2689e30 100644
--- a/src/core/transport/transport.c
+++ b/src/core/transport/transport.c
@@ -85,6 +85,6 @@
     op->cancel_with_status = status;
   }
   if (message) {
-    grpc_mdstr_unref(message);
+    GRPC_MDSTR_UNREF(message);
   }
 }