ath10k: fix failure to send NULL func frame for 10.4

ath10k: fix failure to send NULL func frame for 10.4

commit fcf7cf1551cae54e747a771f5808240f2a37708f upstream.

This partially reverts 'commit 2cdce425aa33
("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: 2cdce425aa33 "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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>