ath10k: Fix bug in max. VHT A-MPDU size

For VHT peers, the maximum A-MPDU size has to be calculated
from the VHT capabilities element and not the HT-cap. The formula
is the same, but a higher value is used in VHT, allowing larger
aggregates to be transmitted.

The patch contains a workaround for some Netgear/Linksys APs that
report Rx A-MPDU factor incorrectly.

Tested-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>