For every peer expose through `getpeerinfo` RPC whether or not we selected them as HB peers, and whether or not they selected us as HB peers.

Suggestion by @gmaxwell.
{
    const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
    size_t nCount = headers.size();
    if (nCount == 0) {
        
        return;
    }
    bool received_new_header = false;
    const CBlockIndex *pindexLast = nullptr;
    {
        LOCK(cs_main);
        CNodeState *nodestate = State(pfrom.GetId());
        
        
        
        
        
        
        
        
        if (!LookupBlockIndex(headers[0].hashPrevBlock) && nCount < MAX_BLOCKS_TO_ANNOUNCE) {
            nodestate->nUnconnectingHeaders++;
            m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, ::ChainActive().GetLocator(pindexBestHeader), uint256()));
            LogPrint(BCLog::NET, "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
                    headers[0].GetHash().ToString(),