mwl8k: Allow adding station interface on AP firmware

When user wants to add a station interface when
AP firmware is loaded & in-use, allow creating
it and also notify user about the same.

Allow adding max one STA interface for AP fw.

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>