wcn36xx: Fix TX data path

This patch contains the following fixes:

- Use correct queue for submitting QoS packet. The queue id to use
is a one-to-one mapping with the TID.

- Don't encrypt a frame with IEEE80211_TX_INTFL_DONT_ENCRYPT flag.

- Use the 'special queue' for null packets, preventing the firmware
to submit it as AMPDU.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1595586052-16081-5-git-send-email-loic.poulain@linaro.org