Fix ScanManagerTest#testMetricsScanRadioDurationScreenOnOff

During screen off, SCAN_MODE_LOW_POWER could be downgraded to
SCAN_MODE_SCREEN_OFF. While changing the scan mode, scan disable/re-enable
can happen and the counter metrics would be updated according to the
scan state toggled. This change is to consider the invocation count by
the changed scan mode.

Bug: 300525973
Test: atest BluetoothInstrumentationTests
Change-Id: I2c88ce39188329e1a5dca67e0a16765bc825be3b