mwifiex: add cfg80211 dump_station handler

This enables user to dump station information using
"iw dev <devname> station dump" command.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>