mwifiex: 11h handling for AP interface

This patch enables 11h extensions in FW upon detecting DFS
channel in start radar detection/channel switch handlers.
Patch also takes care of disabling 11h when non DFS channels
are to be set during start_ap handler.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Qingshui Gao <gaoqs@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>