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()`
Maybe we could make `doInit` final in AMMR and have a new method (not abstract, just empty by default), but I can't think of a good name... `doDoInit`, `moreInit` :smile: