lib/connections: Support setting traffic class (fixes #3790)

vendor/golang.org/x/net/ipv4/syscall_windows.go

@@ -0,0 +1,18 @@
+// Copyright 2016 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.
+
+package ipv4
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func getsockopt(s uintptr, level, name int, v unsafe.Pointer, l *uint32) error {
+	return syscall.Getsockopt(syscall.Handle(s), int32(level), int32(name), (*byte)(v), (*int32)(unsafe.Pointer(l)))
+}
+
+func setsockopt(s uintptr, level, name int, v unsafe.Pointer, l uint32) error {
+	return syscall.Setsockopt(syscall.Handle(s), int32(level), int32(name), (*byte)(v), int32(l))
+}