message: [network] Simplify the property of Discovery
  * Add self "PeerId" so that we can avoid deserializing it again and again
  * Prefix "note" with an underscore as the property is not used for now
  Closes:
  Approved by: phlip9
diff: @@ -84,8 +84,11 @@ pub const DISCOVERY_PROTOCOL_NAME: &[u8] = b"/libra/discovery/0.1.0";
  /// The actor running the discovery protocol.
  pub struct Discovery<TTicker, TSubstream> {
  - /// Note for self.
  - self_note: Note,
  + /// Note for self, which is prefixed with an underscore as this is not used but is in
  + /// preparation for logic that changes the advertised Note while the validator is running.
  + _note: Note,
  + /// PeerId for self.
  + peer_id: PeerId,
  /// Validator for verifying signatures on messages.
  trusted_peers: Arc<RwLock<HashMap<PeerId, NetworkPublicKeys>>>,
  /// Current state, maintaining the most recent Note for each peer, alongside parsed PeerInfo.
  @@ -145,7 +148,8 @@ where
  .into_iter()
  .collect();
  Self {
  - self_note,
  + _note: self_note,
  + peer_id: self_peer_id,
  seed_peers,
  trusted_peers,
  known_peers,
  @@ -163,8 +167,7 @@ where
  // list.
  async fn connect_to_seed_peers(&mut self) {
  debug!("Connecting to seed peers");
  - let self_peer_id =
  - PeerId::try_from(self.self_note.peer_id.clone()).expect("PeerId parsing failed");
  + let self_peer_id = self.peer_id;
  for (peer_id, peer_info) in self
  .seed_peers
  .iter()
  @@ -322,8 +325,6 @@ where
  async fn reconcile(&mut self, remote_peer: PeerId, remote_notes: Vec<VerifiedNote>) {
  // If a peer is previously unknown, or has a newer epoch number, we update its
  // corresponding entry in the map.
  - let self_peer_id =
  - PeerId::try_from(self.self_note.peer_id.clone()).expect("PeerId parsing fails");
  for note in remote_notes {
  match self.known_peers.get_mut(&note.peer_id) {
  // If we know about this peer, and receive the same or an older epoch, we do
  @@ -346,7 +347,7 @@ where
  );
  // We can never receive a note with a higher epoch number on us than what we
  // ourselves have broadcasted.
  - assert_ne!(note.peer_id, self_peer_id);
  + assert_ne!(note.peer_id, self.peer_id);
  // Update internal state of the peer with new Note.
  self.known_peers.insert(note.peer_id, note.clone());
  