journal: fix parsing of facility in syslog messages

journal: fix parsing of facility in syslog messages

In 49998b383 (journald: do not overwrite syslog facility when
parsing priority) journald started ignoring facility part when
reading service stderr to convert to syslog messages. In this
case it is fine, because only the priority is allowed.

But the same codepath is used for syslog messages, where the
facility should be used. Split the two codepaths by explicitly
specyfing whether the facility should be ignored or not.

https://bugzilla.redhat.com/show_bug.cgi?id=988814