mwifiex: add AP command sys_config and set channel

1. support for AP sys_config command and added parsing of channel
information.
2. support for setting AP channel from cfg80211 set_channel handler

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>