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.
std::shared_ptr<const CBlockHeaderAndShortTxIDs> pcmpctblock = std::make_shared<const CBlockHeaderAndShortTxIDs> (*pblock, true);
    const CNetMsgMaker msgMaker(PROTOCOL_VERSION);
    LOCK(cs_main);
    static int nHighestFastAnnounce = 0;
    if (pindex->nHeight <= nHighestFastAnnounce)
        return;
    nHighestFastAnnounce = pindex->nHeight;
    bool fWitnessEnabled = IsWitnessEnabled(pindex->pprev, m_chainparams.GetConsensus());
    uint256 hashBlock(pblock->GetHash());