HTTP/3: fixed ngx_stat_active counter. Previously the counter was not incremented for HTTP/3 streams, but still decremented in ngx_http_close_connection(). There are two solutions here, one is to increment the counter for HTTP/3 streams, and the other one is not to decrement the counter for HTTP/3 streams. The latter solution looks inconsistent with ngx_stat_reading/ngx_stat_writing, which are incremented on a per-request basis. The change adds ngx_stat_active increment for HTTP/3 request and push streams.