Do not emit `upgrade` if the server is just advertising its protocols
support as per RFC 7230 Section 6.7.
A server MAY send an Upgrade header field in any other response
to advertise that it implements support for upgrading to the
listed protocols, in order of descending preference, when
appropriate for a future request.
Fix: https://github.com/nodejs/node/issues/4334
PR-URL: https://github.com/nodejs/node/pull/4337
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
