BT: Don't allow isBleScanAlwaysAvailable API call for non foreground users

When a 3rd app with non-foreground user_id call
enableBLE(), updateBleAppCount() will set mEnableBLE
to true. But the following enable() call is returned
false directly and mEnableBLE is not cleared
because it is non-foreground user. As a result,
the next bt turning-on will be stuck at ble on state.
To fix it, return false directly in
isBleScanAlwaysAvailable for non foreground users,
then updateBleAppCount will not be called in enableBLE().

Change-Id: I77b9dc5ce922986e87dabb70b318a9a07048a659
CRs-Fixed: 2650659