rtlwifi: btcoex: 23b 1ant: check PS state before setting tdma duration

For time division multiple access, the wifi and bt take turns to
transmit, but we need to let AP know that wifi is under standby mode by
sending null data to "pretend" entering power saving state using lps
rpwm.

But, the fw does not know if it is the actual power saving mode or just a
fake one to cheat to the AP. Hence, before fw setting the tdma duration,
the fw needs the driver to check the power saving state first.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Birming Chiu <birming@realtek.com>
Cc: Shaofu <shaofu@realtek.com>
Cc: Steven Ting <steventing@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>