ath9k: Fix sequence numbers for PAE frames

Currently, PAE frames are not assigned proper sequence numbers.
Since sending PAE frames as part of aggregates breaks
crupto with several APs, they are sent as normal MPDUs.
Fix the seqeuence number issue by updating the frame with the
internal sequence number.

Tested-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>