sysutils/syslog-ng: Update to 4.8.1

Updating to 4.8.1 brought in MQTT support. This broke packaging,
requring the addition of an MQTT option.

The patch in its entirety was provided by our upstream who maintains
packaging for various Linux distros and FreeBSD.

Submitted by: Peter Czanik (CzP) <peter.czanik@oneidentity.com>

		Balabit (a OneIdentity company) / syslog-ng upstream