disable keep alive for h2c requests

modules/caddyhttp/reverseproxy/httptransport.go

@@ -439,6 +439,9 @@ func (h *HTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) {
  // if H2C ("HTTP/2 over cleartext") is enabled and the upstream request is
  // HTTP without TLS, use the alternate H2C-capable transport instead
  if req.URL.Scheme == "http" && h.h2cTransport != nil {
+ // There is no dedicated DisableKeepAlives field in *http2.Transport.
+ // This is an alternative way to disable keep-alive.
+ req.Close = h.Transport.DisableKeepAlives
  return h.h2cTransport.RoundTrip(req)
  }