Add health check for DNS

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

@@ -0,0 +1,25 @@
+// Copyright 2014 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
+
+func (f *icmpFilter) accept(typ ICMPType) {
+	f.Data &^= 1 << (uint32(typ) & 31)
+}
+
+func (f *icmpFilter) block(typ ICMPType) {
+	f.Data |= 1 << (uint32(typ) & 31)
+}
+
+func (f *icmpFilter) setAll(block bool) {
+	if block {
+		f.Data = 1<<32 - 1
+	} else {
+		f.Data = 0
+	}
+}
+
+func (f *icmpFilter) willBlock(typ ICMPType) bool {
+	return f.Data&(1<<(uint32(typ)&31)) != 0
+}