Potential issue with max concurrent streams

[cynecx]

See https://github.com/hyperium/hyper/issues/2419.

This can be reproduced "faster" by limiting the max concurrent streams on the server side (go):

import (
	"net/http"
	"golang.org/x/net/http2"
...
)
...
	server := &http.Server{Addr: ":9001", Handler: r, ErrorLog: logger}
	http2.ConfigureServer(server, &http2.Server{
		MaxConcurrentStreams: 4,
	})