HTTP/2: handling of connections initialized during shutdown. If an HTTP/2 connection opened before a graceful shutdown, but ngx_http_v2_init() is called after idle connections were closed, such a connection ended up being open till closed by the client (or up to keepalive_time), delaying shutdown. With this change, such connections are allowed to serve just one request, much like it happens in HTTP/1.x, and closed afterwards. Reported by Kasei Wang, https://freenginx.org/pipermail/nginx-devel/2024-May/000277.html