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.
bool select_recv = !pnode->fPauseRecv;
            bool select_send;
            {
                LOCK(pnode->cs_vSend);
                select_send = !pnode->vSendMsg.empty();
            }
            LOCK(pnode->cs_hSocket);
            if (pnode->hSocket == INVALID_SOCKET)
                continue;
            error_set.insert(pnode->hSocket);
            if (select_send) {
                send_set.insert(pnode->hSocket);
                continue;
            }
            if (select_recv) {
                recv_set.insert(pnode->hSocket);
            }
        }
    }
    return !recv_set.empty() || !send_set.empty() || !error_set.empty();
}
#ifdef USE_POLL
void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
{
    std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
    if (!GenerateSelectSet(recv_select_set, send_select_set, error_select_set)) {
        interruptNet.sleep_for(std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS));
        return;