Motivation:
When more than one connection header is present in h2c upgrade request, upgrade fails. This is to fix that.
Modification:
In HttpServerUpgradeHandler's upgrade() method, check whether any of the connection header value is upgrade, not just the first header value which might return a different value other than upgrade.
Result:
Fixes#8846.
With this PR, now when multiple connection headers are sent with the upgrade request, upgrade will not fail.