The net.tcp.service item (probably net.tcp.service.perf too) does not do a timeout under certain circumstances and blocks an instance of zabbix_agentd (CLOSE_WAIT state).

How reproducible:
Always.

Steps to reproduce:
1. Put "smtpd_recipient_restrictions = fuuuu" into /etc/postfix/main.cf and restart postfix
2. zabbix_get -s 127.0.0.1 -k "net.tcp.service.[smtp]"
3. Repeat above step five times and get a dysfunctional zabbix-agent

Actual results:
Getting item data hangs.

Expected results:
A timeout while getting item net.tcp.service.