There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

#### Useful skills:

* Bitcoin protocol messages
* Bitcoin Core P2P design
* Running our unit and functional tests

#### Want to work on this issue?

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

WITH_LOCK(g_cs_orphans, m_orphanage.EraseForPeer(nodeid));
    m_txrequest.DisconnectedPeer(nodeid);
    nPreferredDownload -= state->fPreferredDownload;
    nPeersWithValidatedDownloads -= (state->nBlocksInFlightValidHeaders != 0);
    assert(nPeersWithValidatedDownloads >= 0);
    m_outbound_peers_with_protect_from_disconnect -= state->m_chain_sync.m_protect;
    assert(m_outbound_peers_with_protect_from_disconnect >= 0);
    m_wtxid_relay_peers -= state->m_wtxid_relay;
    assert(m_wtxid_relay_peers >= 0);
    mapNodeState.erase(nodeid);
    if (mapNodeState.empty()) {
        
        assert(mapBlocksInFlight.empty());
        assert(nPreferredDownload == 0);
        assert(nPeersWithValidatedDownloads == 0);
        assert(m_outbound_peers_with_protect_from_disconnect == 0);
        assert(m_wtxid_relay_peers == 0);
        assert(m_txrequest.Size() == 0);
    }
    } 
    if (node.fSuccessfullyConnected && misbehavior == 0 &&
        !node.IsBlockOnlyConn() && !node.IsInboundConn()) {
        
        
        
        m_addrman.Connected(node.addr);
    }
    LogPrint(BCLog::NET, "Cleared nodestate for peer=%d\n", nodeid);
}
PeerRef PeerManagerImpl::GetPeerRef(NodeId id) const