rtw88: coex: simplify the setting and condition about WLAN TX limitation

Life time related setting is related to WLAN active port number,
not its mode. The original setting may cause poor WLAN performance.

In most case, WLAN TX limitation is helpful for BT in coexistence
scenario, especially for A2DP quality.
So this is necessary to fix the setting and constraint it.

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/20201109085909.9143-12-pkshih@realtek.com