wifi: rtl8xxxu: make supporting AP mode only on port 0 transparent

When the driver is used for concurrent mode, both virtual interfaces can
be set to station or AP mode, though only one can be in AP mode at the
same time.

In order to keep the code simple, use only hw port 0 for AP mode. When
an interface is added in AP mode which would be assigned to port 1, use
a switch_port function to transparently swap the mapping between virtual
interface and hw port.

Signed-off-by: Martin Kaistra <martin.kaistra@linutronix.de>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231222101442.626837-21-martin.kaistra@linutronix.de