Efficiently handle writing ( wrap(...) ) of CompositeByteBuf when using SslHandler

Motivation:

SslHandler.wrap(...) does a poor job when handling CompositeByteBuf as it always call ByteBuf.nioBuffer() which will do a memory copy when a CompositeByteBuf is used that is backed by multiple ByteBuf.

Modifications:

- Use SslEngine.wrap(ByteBuffer[]...) to allow wrap CompositeByteBuf in an efficient manner
- Reduce object allocation in unwrapNonAppData(...)

Result:

Performance improvement when a CompositeByteBuf is written and the SslHandler is in the ChannelPipeline.