Hi,
There is no configuration options in RS232, which can limit number off to connection to serial device. At the moment, only solution I can suggest is to use firewall rules and limit number of connections per TCP port.
Enter following rule in Network -> Firewall -> Custom Rules. This rule will allow only one connection for 2320 port and until first device release connection, no other device will be alowed to connect.
iptables -I INPUT -p tcp --syn --dport 2320 -m connlimit --connlimit-above 1 -j REJECT --reject-with tcp-reset