The ClientRequest function will only report a peer port attribute if
that peer port differs from the standard 80 for HTTP and 443 for HTTPS.
In determining if the request is for HTTPS use the request URL scheme.
This is not perfect. If a user doesn't provide a scheme this will not be
correctly detected. However, the current approach of checking if the
`TLS` field is non-nil will always be wrong, requests made by client
ignore this field and it is always nil. Therefore, switching to using
the URL field is the best we can do without having already made the
request.