cfg80211: Add support for aborting an ongoing scan

Implement new functionality for aborting an ongoing scan.

Add NL80211_CMD_ABORT_SCAN to the nl80211 interface. After
aborting the scan, driver shall provide the scan status by
calling cfg80211_scan_done().

Reviewed-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Vidyullatha Kanchanapally <vkanchan@qti.qualcomm.com>
Signed-off-by: Sunil Dutt <usdutt@qti.qualcomm.com>
[change command to take wdev instead of netdev so that it
 can be used on p2p-device scans]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>