Add syslog-ng321 to list.

Peter Czanik, our upline support person at Balabit for syslog-ng
recommended waiting a week before making syslog-ng321 default. However
Nicolas Embriz <nbari@tequila.io> requested it be made default earlier.
Since there are no issues with syslog-ng321 and our upline sees no issues
with making 321 default, let's make it so.

Requested by: Nicolas Embriz <nbari@tequila.io>
Reviewed by: Peter Czanik (CzP) <peter.czanik@balabit.com>

		Balabit / syslog-ng upstream