vcl_recv
RxReqの処理を書く
https://varnish-cache.org/docs/trunk/users-guide/vcl-built-in-subs.html#vcl-recv
Called at the beginning of a request, after the complete request has been received and parsed, after a restart or as the result of an ESI include.
https://www.varnish-software.com/developers/tutorials/example-vcl-template/#3-host-header-normalization