Parse user flags as flags instead of enum.

The flags field in UserInfo is a int32_t that contains multiple
UserFlags 'or'ed together. We should not parse it as enum.

Test: atest android.hardware.automotive.vehicle@2.0-utils-unit-tests
Bug: 202520478
Change-Id: Ie7e81a8a5f39f6070e35f2e77bce88a211fd526b