ath9k: Fix STA disconnect issue due to received MIC failed bcast frames

ath9k: Fix STA disconnect issue due to received MIC failed bcast frames

commit 916448e77f6bcaaa7f13c3de0c3851783ae2bfd0 upstream.

AR_RxKeyIdxValid will not be set for bcast/mcast frames and so relying
this status for MIC failed frames is buggy.

Due to this, MIC failure events for broadcast frames are not sent to
supplicant resulted in AP disconnecting the STA.

Able to pass Wifi Test case 5.2.18 with this fix.

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>