The value of tVrrpRtUnknEvtType specifies whether
this event is a 'delta' or an 'explicit' event. When the event
is 'set', the value of tVrrpRtUnknEvtPriority will
be subtracted from the in-use priority in case of a 'delta'
event or the in-use priority will be explicitly overridden by
the value of tVrrpRtUnknEvtPriority in case of an
'explicit' event.