private static int padding16(final int size) {
    final int pad = size % 16;
    return pad == 0 ? 0 : 16 - pad;
  }
Frames a message for sending to an RLPx peer, encrypting it and calculating the appropriate
MACs.

@param message The message to frame.
@param output The {@link ByteBuf} to write framed data to.
ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/rlpx/framing/Framer.java