http: make request.abort() destroy the socket

`request.abort()` did not destroy the socket if it was called
before a socket was assigned to the request and the request
did not use an `Agent` or a Unix Domain Socket was used.

Fixes: https://github.com/nodejs/node/issues/10812
PR-URL: https://github.com/nodejs/node/pull/10818


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>