lnwire: add ChannelUpdate2

Add the new ChannelUpdate2 message and ensure that it implements the
ChannelUpdate interface.

lnwire/message.go

@@ -59,6 +59,7 @@ const (
 	MsgReplyChannelRange                   = 264
 	MsgGossipTimestampRange                = 265
 	MsgChannelAnnouncement2                = 267
+	MsgChannelUpdate2                      = 271
 	MsgKickoffSig                          = 777
 )
 
@@ -161,6 +162,8 @@ func (t MessageType) String() string {
 		return "MsgAnnounceSignatures2"
 	case MsgChannelAnnouncement2:
 		return "ChannelAnnouncement2"
+	case MsgChannelUpdate2:
+		return "ChannelUpdate2"
 	default:
 		return "<unknown>"
 	}
@@ -294,6 +297,8 @@ func makeEmptyMessage(msgType MessageType) (Message, error) {
 		msg = &AnnounceSignatures2{}
 	case MsgChannelAnnouncement2:
 		msg = &ChannelAnnouncement2{}
+	case MsgChannelUpdate2:
+		msg = &ChannelUpdate2{}
 	default:
 		// If the message is not within our custom range and has not
 		// specifically been overridden, return an unknown message.