src: use available ReqWrap instance for libuv req

Use available `ReqWrap` descendant to make call to libuv -- avoid doing
call with the `ReqWrap`'s request member and then calling `Dispatched()`
afterwards.

PR-URL: https://github.com/nodejs/node/pull/21980


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>