rename isTrigger to restart-on-upgrade

we're moving away from "trigger" services to "controller" services,
and "restart-on-upgrade" is the name used by s6-rc

modules/ifwait/ifwait.nix

@@ -9,7 +9,7 @@ let
 in longrun {
   name = "ifwait.${interface.name}";
   buildInputs = [ service ];
-  isTrigger = true;
+  restart-on-upgrade = true;
   run = ''
     ${ifwait}/bin/ifwait -s ${service.name}  $(output ${interface} ifname) ${state}
   '';