multi: rename ChannelUpdate to ChannelUpdate1

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

peer/brontide.go

@@ -301,7 +301,7 @@ type Config struct {
 
 	// FetchLastChanUpdate fetches our latest channel update for a target
 	// channel.
-	FetchLastChanUpdate func(lnwire.ShortChannelID) (*lnwire.ChannelUpdate,
+	FetchLastChanUpdate func(lnwire.ShortChannelID) (*lnwire.ChannelUpdate1,
 		error)
 
 	// FundingManager is an implementation of the funding.Controller interface.
@@ -1963,7 +1963,7 @@ out:
 					nextMsg.MsgType())
 			}
 
-		case *lnwire.ChannelUpdate,
+		case *lnwire.ChannelUpdate1,
 			*lnwire.ChannelAnnouncement1,
 			*lnwire.NodeAnnouncement,
 			*lnwire.AnnounceSignatures1,
@@ -2233,7 +2233,7 @@ func messageSummary(msg lnwire.Message) string {
 		return fmt.Sprintf("chain_hash=%v, short_chan_id=%v",
 			msg.ChainHash, msg.ShortChannelID.ToUint64())
 
-	case *lnwire.ChannelUpdate:
+	case *lnwire.ChannelUpdate1:
 		return fmt.Sprintf("chain_hash=%v, short_chan_id=%v, "+
 			"mflags=%v, cflags=%v, update_time=%v", msg.ChainHash,
 			msg.ShortChannelID.ToUint64(), msg.MessageFlags,