acs_cfg is not initialized when sap starts
failed. And acs_cfg is accessed during
Random channel selection when sap interface
gets Radar event.
Fix by checking sap ctx state and acs_cfg
During dfs radar event.
Change-Id: I7e04e1a9e357ccd0b39b4edcc4c8a34b54e388ce
CRs-Fixed: 2174532