wifi: rtw89: coex: Set Bluetooth background scan PTA request priority

When Wi-Fi is RX, set Bluetooth background scan to low-priority and
not to break Wi-Fi packet. Bluetooth can RX depend on hardware ability
even RX request has been rejected. This way can improve Wi-Fi RX
throughput performance.

Signed-off-by: Ching-Te Ku <ku920601@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/20230117114109.4298-6-pkshih@realtek.com