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.
{
    size_t vNodesSize;
    {
        LOCK(cs_vNodes);
        vNodesSize = vNodes.size();
    }
    if(vNodesSize != nPrevNodeCount) {
        nPrevNodeCount = vNodesSize;
        if(clientInterface)
            clientInterface->NotifyNumConnectionsChanged(vNodesSize);
    }
}
void CConnman::InactivityCheck(CNode *pnode)