mac80211: allow scanning for 5/10 MHz channels in IBSS

Use a chandef instead of just the channel for scanning, and enable
5/10 Mhz scanning for IBSS mode. Also reporting is changed to the new
inform_bss functions.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>