The pre-11n calculations include SIFS, but the 11n ones don't.
The reason is that (mostly) the 11n hardware is doing the SIFS calculation
for us but the pre-11n hardware isn't. This means that we're over-shooting
the times in the duration field for non-11n frames on 11n hardware, which
is OK, if not a little inefficient.
Now, this is all fine for what the hardware needs for doing duration math
for ACK, RTS/CTS, frame length, etc, but it isn't useful for doing PHY
duration calculations. Ie, given a frame to TX and its timestamp, what
would the end of the actual transmission time be; and similar for an
RX timestamp and figuring out its original length.
So, this adds a new field to the duration routines which requests
SIFS or no SIFS to be included. All the callers currently will call
it requesting SIFS, so this /should/ be a glorious no-op. I'm however
planning some future work around airtime fairness and positioning which
requires these routines to have SIFS be optional.
Notably though, the 11n version doesn't do any SIFS addition at the moment.
I'll go and tweak and verify all of the packet durations before I go and
flip that part on.
Tested:
* AR9330, STA mode
* AR9330, AP mode
* AR9380, STA mode
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