Remove c->is_resp, keep it private to http.c

tutorials/http/http-reverse-proxy/main.c

@@ -65,7 +65,7 @@ static void fn(struct mg_connection *c, int ev, void *ev_data) {
       }
       c->fn_data = c2;
       forward_request(hm, c2);
-      c->is_resp = 0;  // process further msgs in keep-alive connection
+      c->pfn_data = NULL;  // process further msgs in keep-alive connection
       c2->is_hexdumping = 1;
     }
   } else if (ev == MG_EV_CLOSE) {