Can I limit the number of connections per client in OpenLDAP?
It didn't occur to me until I had already posted the question, but I have found a solution/workaround.
Instead of changing the OpenLDAP server configuration I have told the firewall (iptables in this case, since this is a Linux machine) to limit the number of connections per client to the relevant port. If anyone is interested, the line I have added to /etc/sysconfig/iptables is this:
-A RH-Firewall-1-INPUT -p tcp --dport ldaps -m connlimit --connlimit-above 100 -j REJECT