mwifiex: fix AP start problem for newly added interface

It's been observed that if interface type is changed from managed to
__ap, AP can be successfully started. But there is a problem if new
ap interface is added.

The problem got resolved after sending appropriate commands to firmware
in add_interface handler.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>