ath9k: Fix tx throughput drops for AR9003 chips with AES encryption

commit 4f6760b0 upstream.

While sending aggregated frames in AES, the AR5416 chips
required additional padding b/w subframes. This workaround
is not needed for edma (AR9003 family) chips. With this patch
~4Mbps thoughput improvement was observed in clear environment.

Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>