WifiPermissionsUtil: Clear calling identity before isLocationModeEnabled

For incoming binder calls, ensure we clear the calling identity before
invoking isLocationModeEnabled because it requires system permissions to
check the current user (which the app probably does not have).

Bug: 123254742
Test: CTS tests for LOHS.
Change-Id: Ia73e6c5c2eb75616f0cee4e51d9697144d21a799
2 files changed