rtlwifi: btcoex: 21a 1ant: do not switch antenna when wifi is under 5G channel

When wifi is on a 5G channel, the 5G signal will not interfere bt 2.4G
signal, and they can transmit simultaneously, hence there is no need to
switch antenna between wifi and bt.

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>