tool_cb_wrt.c: disambiguate warning message

src/tool_cb_wrt.c

@@ -57,7 +57,7 @@ size_t tool_write_cb(void *buffer, size_t sz, size_t nmemb, void *userdata)
 #ifdef DEBUGBUILD
   if(config->include_headers) {
     if(sz * nmemb > (size_t)CURL_MAX_HTTP_HEADER) {
-      warnf(config, "Data size exceeds single call write limit!\n");
+      warnf(config, "Header data size exceeds single call write limit!\n");
       return failure;
     }
   }