htlcswitch/link_test: wait for link shutdown after removal

htlcswitch/link_test.go

@@ -3710,6 +3710,7 @@ func (h *persistentLinkHarness) restart(restartSwitch bool,
 
 	// First, remove the link from the switch.
 	h.coreLink.cfg.Switch.RemoveLink(h.link.ChanID())
+	h.coreLink.WaitForShutdown()
 
 	var htlcSwitch *Switch
 	if restartSwitch {