rtlwifi: btcoex: 21a 2ant: monitor wifi counter to check network status

If there are a lot of low-rate packets, then the connection of wifi is
unstable. If so, we should switch resource to bt to have a higher
transmission quality, or wifi resource will be wasted

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Pkshih <pkshih@realtek.com>
Cc: Birming Chiu <birming@realtek.com>
Cc: Shaofu <shaofu@realtek.com>
Cc: Steven Ting <steventing@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>