multi: rename ChannelUpdate to ChannelUpdate1

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

funding/manager.go

@@ -4144,7 +4144,7 @@ func (f *Manager) ensureInitialForwardingPolicy(chanID lnwire.ChannelID,
 // send out to the network after a new channel has been created locally.
 type chanAnnouncement struct {
 	chanAnn       *lnwire.ChannelAnnouncement1
-	chanUpdateAnn *lnwire.ChannelUpdate
+	chanUpdateAnn *lnwire.ChannelUpdate1
 	chanProof     *lnwire.AnnounceSignatures1
 }
 
@@ -4238,7 +4238,7 @@ func (f *Manager) newChanAnnouncement(localPubKey,
 
 	// We announce the channel with the default values. Some of
 	// these values can later be changed by crafting a new ChannelUpdate.
-	chanUpdateAnn := &lnwire.ChannelUpdate{
+	chanUpdateAnn := &lnwire.ChannelUpdate1{
 		ShortChannelID: shortChanID,
 		ChainHash:      chainHash,
 		Timestamp:      uint32(time.Now().Unix()),

funding/manager_test.go

@@ -1210,7 +1210,7 @@ func assertChannelAnnouncements(t *testing.T, alice, bob *testNode,
 			switch m := msg.(type) {
 			case *lnwire.ChannelAnnouncement1:
 				gotChannelAnnouncement = true
-			case *lnwire.ChannelUpdate:
+			case *lnwire.ChannelUpdate1:
 
 				// The channel update sent by the node should
 				// advertise the MinHTLC value required by the