net-mgmt/zabbix5-server: Update to 5.0.16

Release notes: https://www.zabbix.com/rn/rn5.0.16

Approved by: pg@pakhom.spb.ru (maintainer)
Differential Revision: https://reviews.freebsd.org/D32295

(cherry picked from commit c6cfec3e2b440418b76c46a30bd6260ff9dc1f93)