BUG-1675: bump netty version to 4.0.23

Speed and correctness fixes have gone into the releases which we should
include in Helium.

Change-Id: Ie106b6b7bb523cdcf142f9c11341f0ff568c691f
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-1675: bump netty version to 4.0.23"