mwifiex: do not support change AP interface to station mode

Firmware do not support change interface from micro-ap mode
to station mode, forbid this operation

Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>