message: Don't send a message type for responses
diff: @@ -116,16 +116,13 @@ impl Message {
  bytes.put_u64_be(*node_id);
  Data(lwcid, bytes.freeze())
  }
  - Message::GetBlockHeaders(lwcid, gbh) => {
  - Data(lwcid, MessageType::MsgGetHeaders.encode_with(&gbh))
  - }
  - Message::BlockHeaders(lwcid, bh) => {
  - Data(lwcid, MessageType::MsgHeaders.encode_with(&bh))
  - }
  - Message::GetBlocks(lwcid, gb) => {
  - Data(lwcid, MessageType::MsgGetBlocks.encode_with(&gb))
  - }
  - Message::Block(lwcid, b) => Data(lwcid, MessageType::MsgBlock.encode_with(&b)),
  + Message::GetBlockHeaders(lwcid, gbh) =>
  + Data(lwcid, MessageType::MsgGetHeaders.encode_with(&gbh)),
  + Message::BlockHeaders(lwcid, bh) =>
  + Data(lwcid, cbor!(&bh).unwrap().into()),
  + Message::GetBlocks(lwcid, gb) =>
  + Data(lwcid, MessageType::MsgGetBlocks.encode_with(&gb)),
  + Message::Block(lwcid, b) => Data(lwcid, cbor!(&b).unwrap().into()),
  Message::Subscribe(lwcid, keep_alive) => {
  let keep_alive : u64 = if keep_alive { 43 } else { 42 };
  Data(lwcid, MessageType::MsgSubscribe1.encode_with(&keep_alive))
  