This commit really is "fix the OFDM duration calculation to match reality when
running in 802.11g mode."
The AR5212 init vals set AR_MISC_MODE to 0x0 and all the bits that can be set are
set through code.
The AR5416 and later initvals set AR_MISC_MODE to various other values (with
the AR5212 AR_MISC_MODE options cleared), which include AR_PCU_CCK_SIFS_MODE .
This adds 6uS to SIFS on non-CCK frames when transmitting.
This fixes the issue where _DATA_ 802.11g OFDM frames were being TX'ed with
the ACK duration set to 38uS, not 44uS as on the AR5212 (and other devices.)
The AR5212 TX pathway obeys the software-programmed duration field in the packet,
but the 11n TX pathway overrides that with a hardware-calculated duration. This
was getting it wrong because of the above AR_MISC_MODE setting. I've verified
that 11g data OFDM frames are now being TXed with the correct ACK+SIFS duration
programmed in.
e85dde4087