http: move free socket error handling to agent

The http client should not know anything about free sockets. Let
the agent handle its pool of sockets.

PR-URL: https://github.com/nodejs/node/pull/32003


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>