HTTP/3: fixed decoder stream stubs. Now ngx_http_v3_ack_header() and ngx_http_v3_inc_insert_count() always generate decoder error. Our implementation does not use dynamic tables and does not expect client to send Section Acknowledgement or Insert Count Increment. Stream Cancellation, on the other hand, is allowed to be sent anyway. This is why ngx_http_v3_cancel_stream() does not return an error.