We want close non-active connection to avoid fd run out. https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_timeout

I can open a PR if you accept.

1. increment number when there has stream https://github.com/nginx/nginx/blob/43191be96fb5f425710400e0064c0f2d285a352d/src/http/v2/ngx_http_v2.c#L3097
2. when hit timeout, check whether has stream active, or close h2 connection. https://github.com/nginx/nginx/blob/43191be96fb5f425710400e0064c0f2d285a352d/src/http/v2/ngx_http_v2.c#L629