net/http/cgi: set SERVER_PORT to 443 when req.TLS != nil
A hostname without a port leaves the port implied by the protocol.
For HTTPS, the implied port is 443, not 80.
Change-Id: I873a076068f84c8041abf10a435d9499635730a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/454975
Auto-Submit: Damien Neil <dneil@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>