http: detach socket from IncomingMessage on keep-alive

If the socket is not detached then a future call to res.destroy
(through e.g. pipeline) would unecessarily kill the socket while
its in the agent free list.

PR-URL: https://github.com/nodejs/node/pull/32153


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>