wcn36xx: Use sequence number allocated by mac80211

Instead of using the firmware generated sequence number, use the one
already allocated by the mac80211 layer. This allows better control
of the sequence numbers and avoid to rely on same sequence for Data,
QOS Data and QOS Null Data packets.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1595586052-16081-7-git-send-email-loic.poulain@linaro.org