in an 802.11 unicast data packet is equal to the duration of the
SIFS and Acknowledgement. That is, the amount of time reserved
*after* the packet has finished transmitting.
Change the arguments to ieee80211_compute_duration: pass the entire
packet length, not just the payload length. Add a 'debug' argument
to ieee80211_compute_duration and its helper subroutine,
ieee80211_compute_duration1.
If debug != 0, ieee80211_compute_duration printfs its arguments
and several local variables.
In rtw(4), load the 802.11 Duration field with the result from
ieee80211_compute_duration.