Configure http2 with higher maxconcurrent streams (#7363)

This value is needed for Minio's internode communication,
read the meaning of this value as per the HTTP 2.0 spec

https://http2.github.io/http2-spec/#rfc.section.5.1.2

vendor/golang.org/x/net/http2/go111.go

@@ -0,0 +1,29 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.11
+
+package http2
+
+import (
+	"net/http/httptrace"
+	"net/textproto"
+)
+
+func traceHasWroteHeaderField(trace *httptrace.ClientTrace) bool {
+	return trace != nil && trace.WroteHeaderField != nil
+}
+
+func traceWroteHeaderField(trace *httptrace.ClientTrace, k, v string) {
+	if trace != nil && trace.WroteHeaderField != nil {
+		trace.WroteHeaderField(k, []string{v})
+	}
+}
+
+func traceGot1xxResponseFunc(trace *httptrace.ClientTrace) func(int, textproto.MIMEHeader) error {
+	if trace != nil {
+		return trace.Got1xxResponse
+	}
+	return nil
+}