ath10k: adjust the RX packet pad offset at QCA99X0 4addr mode

The QCA99X0 4 addresses RX packets pad 2 bytes at the beginning of
MSDU instead the end of ieee80211 header to keep alignment. The currently RX
data path can't parse the header correctly in this case. This patch fixes it
for QCA99X0.

Signed-off-by: Yanbo Li <yanbol@qca.qualcomm.com>
[kvalo@qca.qualcomm.com: checkpatch fixes and naming changes]
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>