net-mgmt/zabbix32-*: Update to 3.2.8

Update CONFLICTS to also match zabbix[22|34]. [1]
Improve LICENSE.
Remove unnecessary information from the slave ports.

Changes: https://www.zabbix.com/rn3.2.8

PR: 222808
PR: 222317 [1]
Approved by: Pakhom Golynga <pg@pakhom.spb.ru> (maintainer)
Submitted by: Franco Fichtner <franco@opnsense.org> [1]