rtlwifi: btcoex: settings before firmware is downloaded

The btcoex is sometimes unstable because there are some unexpected
behaviors before the firmware has been downloaded successfully.

Therefore we force the antenna path settings to avoid this, then let the
firmware control the btcoexistence when the firmware is ready.

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Ping-Ke Shih <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>