[chore] Validate/set account domain (#619)

* add miekg/dns dependency

* set/validate accountDomain

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

@@ -0,0 +1,44 @@
+// 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
+
+import "golang.org/x/net/internal/socket"
+
+// Sticky socket options
+const (
+	ssoTOS                = iota // header field for unicast packet
+	ssoTTL                       // header field for unicast packet
+	ssoMulticastTTL              // header field for multicast packet
+	ssoMulticastInterface        // outbound interface for multicast packet
+	ssoMulticastLoopback         // loopback for multicast packet
+	ssoReceiveTTL                // header field on received packet
+	ssoReceiveDst                // header field on received packet
+	ssoReceiveInterface          // inbound interface on received packet
+	ssoPacketInfo                // incbound or outbound packet path
+	ssoHeaderPrepend             // ipv4 header prepend
+	ssoStripHeader               // strip ipv4 header
+	ssoICMPFilter                // icmp filter
+	ssoJoinGroup                 // any-source multicast
+	ssoLeaveGroup                // any-source multicast
+	ssoJoinSourceGroup           // source-specific multicast
+	ssoLeaveSourceGroup          // source-specific multicast
+	ssoBlockSourceGroup          // any-source or source-specific multicast
+	ssoUnblockSourceGroup        // any-source or source-specific multicast
+	ssoAttachFilter              // attach BPF for filtering inbound traffic
+)
+
+// Sticky socket option value types
+const (
+	ssoTypeIPMreq = iota + 1
+	ssoTypeIPMreqn
+	ssoTypeGroupReq
+	ssoTypeGroupSourceReq
+)
+
+// A sockOpt represents a binding for sticky socket option.
+type sockOpt struct {
+	socket.Option
+	typ int // hint for option value type; optional
+}