Add health check for DNS

vendor/golang.org/x/net/internal/socket/cmsghdr.go

@@ -0,0 +1,11 @@
+// Copyright 2017 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 aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package socket
+
+func (h *cmsghdr) len() int { return int(h.Len) }
+func (h *cmsghdr) lvl() int { return int(h.Level) }
+func (h *cmsghdr) typ() int { return int(h.Type) }