multi: rename ChannelUpdate to ChannelUpdate1

In preparation for adding a new ChannelUpdate2 message and a
ChannelUpdate interface, we rename the existing message to
ChannelUpdate1.

discovery/message_store_test.go

@@ -59,8 +59,8 @@ func randAnnounceSignatures() *lnwire.AnnounceSignatures1 {
 	}
 }
 
-func randChannelUpdate() *lnwire.ChannelUpdate {
-	return &lnwire.ChannelUpdate{
+func randChannelUpdate() *lnwire.ChannelUpdate1 {
+	return &lnwire.ChannelUpdate1{
 		ShortChannelID:  lnwire.NewShortChanIDFromInt(rand.Uint64()),
 		ExtraOpaqueData: make([]byte, 0),
 	}
@@ -118,7 +118,7 @@ func TestMessageStoreMessages(t *testing.T) {
 			switch msg := msg.(type) {
 			case *lnwire.AnnounceSignatures1:
 				shortChanID = msg.ShortChannelID.ToUint64()
-			case *lnwire.ChannelUpdate:
+			case *lnwire.ChannelUpdate1:
 				shortChanID = msg.ShortChannelID.ToUint64()
 			default:
 				t.Fatalf("found unexpected message type %T", msg)