AdapterServiceTest: Fix flaky test

The scan mode is set after a callback comming from the native.
The java test need to be patient with  the native since it is running on
a uncontrolled thread ¯\_(ツ)_/¯

Bug: 292141273
Bug: 292173583
Test: atest AdapterServiceTest#enable_isCorrectScanMode (x100000)
Change-Id: I4012769d4e54f94299bd85484bdd74a3249c1a06