Some commands always set duration to 0

Seen agaainst 7.6-1986 and later.

Some commands are returning the duration flexible frame but with the value always set to 0. GetAndTouch certainly does this but I've seen some other commands do it too - I can track down which if required.

I've attached a pcap of an example GetAndTouch, note that a Get immediately following returned a duration of 100usec.