http: relax requirements on upgrade listener

The http spec does not say anything about Upgrade headers making
protocol switch mandatory but Node.js implements them as if they
are. Relax the requirements to only destroy the socket if no
upgrade listener exists on the client when status code is 101.

PR-URL: https://github.com/nodejs/node/pull/19981
Fixes: https://github.com/nodejs/node/issues/11552
Refs: https://tools.ietf.org/html/rfc7230#section-6.7


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>