src: make debugger listen on 127.0.0.1 by default

CVE-2018-12120

Backport of 8e7cbe25 to v6.x
Prepared by Sam Roberts <vieuxtech@gmail.com>

Original commit:
  Commit 22720524 ("net: bind to `::` TCP address by default") from
  April 2014 seems to have accidentally changed the default listen
  address from 127.0.0.1 to 0.0.0.0, a.k.a. the "any" address.

  From a security viewpoint it's undesirable to accept debug agent
  connections from anywhere so let's change that back.  Users can
  override the default with the `--debug=<host>:<port>` switch.

  Fixes: https://github.com/nodejs/node/issues/8081
  PR-URL: https://github.com/nodejs/node/pull/8106


Reviewed-By: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs-private/node-private/pull/148


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>