lnwallet: use custom LockTime for rbf coop close

lnwallet/chancloser/rbf_coop_transitions.go

@@ -902,6 +902,7 @@ func (l *RemoteCloseStart) ProcessEvent(event ProtocolEvent, env *Environment,
 
 		chanOpts := []lnwallet.ChanCloseOpt{
 			lnwallet.WithCustomSequence(mempool.MaxRBFSequence),
+			lnwallet.WithCustomLockTime(msg.SigMsg.LockTime),
 		}
 
 		chancloserLog.Infof("responding to close w/ local_addr=%x, "+