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.
if (m_tx_relay != nullptr) {
        LOCK(m_tx_relay->cs_filter);
        stats.fRelayTxes = m_tx_relay->fRelayTxes;
    } else {
        stats.fRelayTxes = false;
    }
    X(nLastSend);
    X(nLastRecv);
    X(nLastTXTime);
    X(nLastBlockTime);
    X(nTimeConnected);
    X(nTimeOffset);
    stats.addrName = GetAddrName();
    X(nVersion);
    {
        LOCK(cs_SubVer);
        X(cleanSubVer);
    }
    stats.fInbound = IsInboundConn();
    stats.m_manual_connection = IsManualConn();
    X(nStartingHeight);
    {
        LOCK(cs_vSend);
        X(mapSendBytesPerMsgCmd);
        X(nSendBytes);
    }
    {
        LOCK(cs_vRecv);
        X(mapRecvBytesPerMsgCmd);
        X(nRecvBytes);