rtlwifi: btcoex: Add rate table for the use of btcoex

The btcoex use the rate to rsolve IOT issue that some APs reduce TX
rate quickly, so it uses the RX rate as a clue to decide TDMA.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Acked-by: Larry Finger <Larry.Finger#lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>