Update current BSS level when signal change event occurs

Update current BSS level when signal change event occurs

When an EVENT_SIGNAL_CHANGE occurs the bgscan is informed about this
change but the new RSSI value is not stored. In consequence, when
roaming candidates are evaluated, the RSSI value of the current BSS used
to compare is an old one obtained during the last scan rather than the
new one given by the signal change event. This leads sometimes to bad
decision when selecting a new BSS for roaming.

This patch solves the issue by updating the current BSS level when
receiving a signal change event in order to have a very up-to-date
current signal value when choosing an new BSS.

Signed-off-by: Matthieu Mauger <matthieux.mauger@intel.com>