ath9k: Fix issue with parsing malformed CFP IE

All QCA chips have the ability to parse the CF Parameter Set
IE in beacons. If the IE is malformed in the beacons from some
APs [1], the HW locks up. In AP mode, a beacon stuck would happen
and in client mode, a disconnection usually is the result.

To fix this issue, set the AR_PCU_MISC_MODE2_CFP_IGNORE to ignore
the CFP IE in beacons - this is applicable for all chips. For
AP mode, if this issue happens, the NAV is also corrupted and has
to be reset - this will be done in a subsequent patch.

[1] : http://msujith.org/ath9k/cfp/Malformed-CF-Param.png

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>