wifi: rtw89: mac: update RTS threshold according to chip gen

When TX size or time of packet over RTS threshold set by this register,
hardware will use RTS protection automatically. Since WiFi 6 and 7 chips
have different register address for this, separate the address according
to chip gen.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231012021455.19816-2-pkshih@realtek.com