rtlwifi: btcoex: Add customer_id to do special deal to oem vendor

Add customer_id field in structure, and then this is a clue to implement
the behavior defined by vendor LENOVO_CHINA.

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>