message: add total difficulty
diff: @@ -306,6 +306,7 @@ impl Inner {
  let peer_info = PeerInfo::new(peer_id.clone().into());
  let block_hash = block.header().id();
  let block_number = block.header().number();
  +
  if let Some(peer_info) = self.peers.lock().await.get_mut(&peer_id) {
  peer_info.peer_info.block_number = block_number;
  peer_info.peer_info.block_id = block_hash;
  @@ -449,7 +450,7 @@ impl Handler<SystemEvents> for NetworkActor {
  let block_hash = block.header().id();
  let block_number = block.header().number();
  - let _total_difficulty = block.get_total_difficulty();
  + let total_difficulty = block.get_total_difficulty();
  let msg = PeerMessage::Block(block.get_block().clone());
  let bytes = msg.encode().unwrap();
  @@ -457,6 +458,7 @@ impl Handler<SystemEvents> for NetworkActor {
  for (peer_id, mut peer_info) in peers.lock().await.iter_mut() {
  peer_info.peer_info.block_number = block_number;
  peer_info.peer_info.block_id = block_hash;
  + peer_info.peer_info.total_difficult = total_difficulty;
  if !peer_info.known_blocks.contains(&id) {
  peer_info.known_blocks.put(id.clone(), ());
  