rtw88: coex: set 4 slot TDMA for BT link and WL busy

To protect both of WL/BT performance while BT is under re-link state.
4-slot mode TDMA can make the re-link more sensitive and mitigate the WL
throughput drop.

Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210112021135.3823-1-pkshih@realtek.com