tls: better error message for socket disconnect

The error emitted when a connection is closed before the
TLS handshake completes seemed rather unspefic by just saying
`socket hang up`.

Use a more verbose message, that also indicates that this is
a purely client-side error, and remove a misleading comment.

PR-URL: https://github.com/nodejs/node/pull/18989


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>