/* compares data mappings, excluding vdr_rpu_id */
static int cmp_data_mapping(const AVDOVIDataMapping *m1,
                            const AVDOVIDataMapping *m2)
{
    static_assert(offsetof(AVDOVIDataMapping, vdr_rpu_id) == 0, "vdr_rpu_id is first field");
    const uint8_t *p1 = &m1->vdr_rpu_id + 1, *p2 = &m2->vdr_rpu_id + 1;
    return memcmp(p1, p2, sizeof(AVDOVIDataMapping) - sizeof(*p1));
}