mwifiex: add cfg80211 testmode support

This patch adds cfg80211 testmode support so that userspace tools can
download necessary commands to firmware during manufacturing mode tests.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>