Support sync fence in NNAPI am: 12ea0d4ed6 am: cf043b51fa

Change-Id: I81e26904d956655628daacb038ad16758a5ad272
diff --git a/wifi/1.3/default/wifi.cpp b/wifi/1.3/default/wifi.cpp
index 2f21819..4229d35 100644
--- a/wifi/1.3/default/wifi.cpp
+++ b/wifi/1.3/default/wifi.cpp
@@ -124,6 +124,8 @@
             }
         }
         LOG(ERROR) << "Wifi HAL start failed";
+        // Clear the event callback objects since the HAL start failed.
+        event_cb_handler_.invalidate();
     }
     return wifi_status;
 }
@@ -158,6 +160,8 @@
         }
         LOG(ERROR) << "Wifi HAL stop failed";
     }
+    // Clear the event callback objects since the HAL is now stopped.
+    event_cb_handler_.invalidate();
     return wifi_status;
 }