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

* add miekg/dns dependency

* set/validate accountDomain

vendor/golang.org/x/net/ipv6/genericopt.go

@@ -0,0 +1,56 @@
+// Copyright 2013 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 ipv6
+
+// TrafficClass returns the traffic class field value for outgoing
+// packets.
+func (c *genericOpt) TrafficClass() (int, error) {
+	if !c.ok() {
+		return 0, errInvalidConn
+	}
+	so, ok := sockOpts[ssoTrafficClass]
+	if !ok {
+		return 0, errNotImplemented
+	}
+	return so.GetInt(c.Conn)
+}
+
+// SetTrafficClass sets the traffic class field value for future
+// outgoing packets.
+func (c *genericOpt) SetTrafficClass(tclass int) error {
+	if !c.ok() {
+		return errInvalidConn
+	}
+	so, ok := sockOpts[ssoTrafficClass]
+	if !ok {
+		return errNotImplemented
+	}
+	return so.SetInt(c.Conn, tclass)
+}
+
+// HopLimit returns the hop limit field value for outgoing packets.
+func (c *genericOpt) HopLimit() (int, error) {
+	if !c.ok() {
+		return 0, errInvalidConn
+	}
+	so, ok := sockOpts[ssoHopLimit]
+	if !ok {
+		return 0, errNotImplemented
+	}
+	return so.GetInt(c.Conn)
+}
+
+// SetHopLimit sets the hop limit field value for future outgoing
+// packets.
+func (c *genericOpt) SetHopLimit(hoplim int) error {
+	if !c.ok() {
+		return errInvalidConn
+	}
+	so, ok := sockOpts[ssoHopLimit]
+	if !ok {
+		return errNotImplemented
+	}
+	return so.SetInt(c.Conn, hoplim)
+}