message: fix: n_sync increase unexpect
diff: @@ -660,10 +660,12 @@ impl<CS: ChainStore> Synchronizer<CS> {
  {
  let mut state = self.peers.state.write();
  if let Some(mut peer_state) = state.get_mut(&peer) {
  + if !peer_state.sync_started {
  peer_state.sync_started = true;
  + self.n_sync.fetch_add(1, Ordering::Release);
  + }
  }
  }
  - self.n_sync.fetch_add(1, Ordering::Release);
  self.send_getheaders_to_peer(nc, peer, &tip);
  }
  