@Override
    protected ByteBuf allocateBuffer(ChannelHandlerContext ctx, ByteBuf msg, boolean preferDirect)
      throws Exception {
      if (preferDirect) {
        return ctx.alloc().directBuffer(msg.readableBytes());
      } else {
        return ctx.alloc().buffer(msg.readableBytes());
      }
    }
Create a ByteString from byte array without copying (wrap), and then set it as the payload
for the builder.
@param builder builder for HDFS DataTransferEncryptorMessage.
@param payload byte array of payload.
hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/FanOutOneBlockAsyncDFSOutputSaslHelper.java