multi: rename ChannelUpdate to ChannelUpdate1

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

routing/router.go

@@ -288,7 +288,7 @@ type Config struct {
 
 	// ApplyChannelUpdate can be called to apply a new channel update to the
 	// graph that we received from a payment failure.
-	ApplyChannelUpdate func(msg *lnwire.ChannelUpdate) bool
+	ApplyChannelUpdate func(msg *lnwire.ChannelUpdate1) bool
 
 	// ClosedSCIDs is used by the router to fetch closed channels.
 	//
@@ -1329,9 +1329,9 @@ func (r *ChannelRouter) sendPayment(ctx context.Context,
 
 // extractChannelUpdate examines the error and extracts the channel update.
 func (r *ChannelRouter) extractChannelUpdate(
-	failure lnwire.FailureMessage) *lnwire.ChannelUpdate {
+	failure lnwire.FailureMessage) *lnwire.ChannelUpdate1 {
 
-	var update *lnwire.ChannelUpdate
+	var update *lnwire.ChannelUpdate1
 	switch onionErr := failure.(type) {
 	case *lnwire.FailExpiryTooSoon:
 		update = &onionErr.Update