wlan: Add periodic scan stop condition for Stickiness issue.

In case of 11K roaming, periodic scan is stop,
when user triggers a scan, when neighbor lookup up
and neighbor lookup down event is recevived and
when host gets candidate with better RSSI.

Change-Id: I332848a68e80aeefbcea3ba0fe1cb6a0b6655d39
CRs-Fixed: 3177944