INT-3431: Fix `RecipientListRouter.onInit()`

JIRA: https://jira.spring.io/browse/INT-3431

The introduced `late channel resolution by name` via https://jira.spring.io/browse/INT-3324
has lost `onInit()` propagation from `RecipientListRouter.onInit()`
Well, I don't think we should spend too much time on it; just that this is not the fist time that someone "forgot" to call `super.oninit()` and there's not much point in making the change if we don't make it better, so maybe we should just go with the 4.0.x fix - it's your call.