wifi: rtl8xxxu: support setting linktype for both interfaces

To prepare for concurrent mode, enhance the set_linktype function to be
able to set the linktype in the MSR register for both hardware ports.

Until the users of set_linktype can handle multiple interfaces, use
port_num = 0.

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/20231222101442.626837-4-martin.kaistra@linutronix.de