lnwallet/chancloser: use block height as lock time for rbf-coop

lnwallet/chancloser/rbf_coop_states.go

@@ -294,6 +294,9 @@ type Environment struct {
 	// ChanType is the type of channel we're attempting to close.
 	ChanType channeldb.ChannelType
 
+	// BlockHeight is the current block height.
+	BlockHeight uint32
+
 	// DefaultFeeRate is the fee we'll use for the closing transaction if
 	// the user didn't specify an ideal fee rate. This may happen if the
 	// remote party is the one that initiates the co-op close.

lnwallet/chancloser/rbf_coop_transitions.go

@@ -716,9 +716,7 @@ func (l *LocalCloseStart) ProcessEvent(event ProtocolEvent, env *Environment,
 			Msgs: []lnwire.Message{&lnwire.ClosingComplete{
 				ChannelID:   env.ChanID,
 				FeeSatoshis: absoluteFee,
-				// TODO(roasbeef): thread thru proper height
-				// value
-				LockTime:    mempool.MaxRBFSequence,
+				LockTime:    env.BlockHeight,
 				ClosingSigs: closingSigs,
 			}},
 		}}