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 bPingFinished = false;
        std::string sProblem;
        if (nAvail >= sizeof(nonce)) {
            vRecv >> nonce;
            
            if (pfrom.nPingNonceSent != 0) {
                if (nonce == pfrom.nPingNonceSent) {
                    
                    bPingFinished = true;
                    const auto ping_time = ping_end - pfrom.m_ping_start.load();
                    if (ping_time.count() >= 0) {
                        
                        pfrom.nPingUsecTime = count_microseconds(ping_time);
                        pfrom.nMinPingUsecTime = std::min(pfrom.nMinPingUsecTime.load(), count_microseconds(ping_time));
                    } else {
                        
                        sProblem = "Timing mishap";
                    }
                } else {
                    
                    sProblem = "Nonce mismatch";
                    if (nonce == 0) {
                        
                        bPingFinished = true;
                        sProblem = "Nonce zero";
                    }
                }
            } else {
                sProblem = "Unsolicited pong without ping";
            }