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.

};
static std::map<NodeId, CNodeState> mapNodeState GUARDED_BY(cs_main);
static CNodeState *State(NodeId pnode) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
    std::map<NodeId, CNodeState>::iterator it = mapNodeState.find(pnode);
    if (it == mapNodeState.end())
        return nullptr;
    return &it->second;
}
static bool RelayAddrsWithPeer(const Peer& peer)
{
    return peer.m_addr_known != nullptr;
}
/**
 * Whether the peer supports the address. For example, a peer that does not
 * implement BIP155 cannot receive Tor v3 addresses because it requires
 * ADDRv2 (BIP155) encoding.
 */
static bool IsAddrCompatible(const Peer& peer, const CAddress& addr)