NioServerBossPool : init() must be called after super(...) otherwise thr...

...ead name determiner is not used

Hi all,

While i was trying to customize thread name i realized that the ThreadNameDeterminer in NioServerBossPool is not used.
This is because the thread is started by the parent class before ```java this.determiner = determiner;``` is called.

This pull request provides a JUnit test that show the issue and respects the rules on the page https://netty.io/Documentation/Developer+Guide

Thanks for your great work.