mwifiex: delete IEs when stop_ap

Delete custom IEs set by start_ap cfg80211 handler when stop_ap
handler is called for AP interface.
IE index required for deletion is stored in mwifiex_private
structure.

Signed-off-by: Avinash Patil <patila@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>