rtlwifi: rtl8723be: Add antenna select module parameter

A number of new laptops have been delivered with only a single antenna.
In principle, this is OK; however, a problem arises when the on-board
EEPROM is programmed to use the other antenna connection. The option
of opening the computer and moving the connector is not always possible
as it will void the warranty in some cases. In addition, this solution
breaks the Windows driver when the box dual boots Linux and Windows.

A fix involving a new module parameter has been developed.  This commit
adds the new parameter and implements the changes needed for the driver.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org> [V4.0+]
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>