Fix bug #2848 - Recycler maxCapacity can be ignored

`Recycler.Stack.push()` allows caching more objects than `maxCapacity` if `maxCapacity` is not a power of two.
you are missing an `a` after `Cap` in the name :-). Also we usually use javadoc comments like this

```
/**
  * Test for issue https://github.com/netty/netty/issues/2848
  */