mwifiex: channel statistics support for mwifiex

This patch adds support to record channel statistics during
scan. With extended scan, scan results are returned as events from
FW while channel statistics are part of scan command response.
We store these channel statistics in adapter.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Xinmin Hu <huxm@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>