mac80211: no BSS changes to driver from beacons processed during scanning

There is no need to send BSS changes to driver from beacons processed
during scanning. We are more interested in beacons from an AP with which
we are associated - these will still be used to send updates to driver as
the beacons are received without scanning.

This change·removes the requirement that bss_info_changed needs to be atomic.
The beacons received during scanning are processed from a tasklet, but if we
do not call bss_info_changed for these beacons there is no need for it to be
atomic. This function (bss_info_changed) is called either from workqueue or
ioctl in all other instances.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>