chanbackup: create new Single version for tweakless commitment chans

In this commit, we create a new Single version for channels that use the
tweakless commitment scheme. When recovering from an SCB into an open
channel shell, we'll now check this field and use it to determine the
proper channel type. Otherwise, we may attempt to sweep the on chain
funds using the commitment point, when it goes directly to our key, or
the other way around.

chanrestore.go

@@ -83,9 +83,23 @@ func (c *chanDBRestorer) openChannelShell(backup chanbackup.Single) (
 		return nil, fmt.Errorf("unable to derive htlc key: %v", err)
 	}
 
+	var chanType channeldb.ChannelType
+	switch backup.Version {
+
+	case chanbackup.DefaultSingleVersion:
+		chanType = channeldb.SingleFunder
+
+	case chanbackup.TweaklessCommitVersion:
+		chanType = channeldb.SingleFunderTweakless
+
+	default:
+		return nil, fmt.Errorf("unknown Single version: %v", err)
+	}
+
 	chanShell := channeldb.ChannelShell{
 		NodeAddrs: backup.Addresses,
 		Chan: &channeldb.OpenChannel{
+			ChanType:                chanType,
 			ChainHash:               backup.ChainHash,
 			IsInitiator:             backup.IsInitiator,
 			Capacity:                backup.Capacity,