net-mgmt/zabbix3-server: Simplify FreeBSD 9 SSL check, ignore LibreSSL

Zabbix3-server can't be built by LibreSSL because it uses PSK. It also
can't be built by FreeBSD 9 base OpenSSL. The latter was documented, but
the solution in the notification was incorrect, so improve all that.

Approved by: SSL blanket