Revert "[#2761] ChannelOutboundBuffer can cause data-corruption because of caching ByteBuffers"

This reverts commit 4059c9f3549753119576a287492dd70ae4742988.
[#2761] Proper work-around for data-corruption caused by cached ByteBuffers

Motivation:

The previous fix did disable the caching of ByteBuffers completely which can cause performance regressions. This fix makes sure we use nioBuffers() for all writes in NioSocketChannel and so prevent data-corruptions. This is still kind of a workaround which will be replaced by a more fundamental fix later.

Modifications:

- Revert 4059c9f3549753119576a287492dd70ae4742988
- Use nioBuffers() for all writes to prevent data-corruption

Result:

No more data-corruption but still retain the original speed.