ZOOKEEPER-3794: upgrade netty to address CVE-2020-11612 - fixed file rename typo

I borked the rename of the netty-codec file on the original submit. This fixes by renaming the one file appropriately.

Change-Id: Ifff1e7bb49b3d0a5816ee97161a4043be7cdaaa6

Author: Patrick Hunt <phunt@apache.org>

Reviewers: Mate Szalay-Beko <symat@apache.org>

Closes #1333 from phunt/ZOOKEEPER-3794_rename