ath10k: fix failure to send NULL func frame for 10.4

This partially reverts 'commit 2cdce425
("ath10k: Fix broken NULL func data frame status for 10.4")'
Unfortunately this breaks sending NULL func and the existing
issue of obtaining proper tx status for NULL function will be
fixed. Also update the comments for feature flag added to be
useless and not working

Fixes: 2cdce425 "ath10k: Fix broken NULL func data frame status for
10.4"
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>