Fix implicit-fallthrough warnings. DO NOT MERGE.

These changes are not needed in goog/master.

Test: make checkbuild
Bug: 112564944
Change-Id: I4f1727d9b33108d34d314787460aa1d2298ae5b2

wifi/1.2/default/wifi_legacy_hal.cpp

@@ -550,6 +550,7 @@ wifi_error WifiLegacyHal::startGscan(
                 }
                 // Fall through if failed. Failure to retrieve cached scan
                 // results should trigger a background scan failure.
+                [[fallthrough]];
                 case WIFI_SCAN_FAILED:
                     on_failure_user_callback(id);
                     on_gscan_event_internal_callback = nullptr;