**Describe what's wrong**

UDF functions are global objects. Creating or dropping them requires global level privilege.

- https://clickhouse.com/docs/en/sql-reference/statements/create/function/
- https://github.com/ClickHouse/ClickHouse/blob/14811a357e2136ff2940d791f2dbe59c65e87601/tests/integration/test_access_for_functions/test.py#L22

But "system.privileges" table reports DATABASE level for these privileges.

```
SELECT
    privilege,
    level
FROM system.privileges
WHERE CAST(privilege, 'text') LIKE '%FUNCTION%'

┌─privilege──────────────┬─level────┐
│ CREATE FUNCTION        │ DATABASE │
│ DROP FUNCTION          │ DATABASE │
│ SYSTEM RELOAD FUNCTION │ GLOBAL   │
└────────────────────────┴──────────┘
```

**Does it reproduce on recent release?**

Actual for the latest versions and master. In particular, for 21.12.4.1.

#include <gtest/gtest.h>
#include <Access/AccessRights.h>
using namespace DB;
TEST(AccessRights, Union)
{
    AccessRights lhs, rhs;
    lhs.grant(AccessType::CREATE_TABLE, "db1", "tb1");
    rhs.grant(AccessType::SELECT, "db2");
    lhs.makeUnion(rhs);
    ASSERT_EQ(lhs.toString(), "GRANT CREATE TABLE ON db1.tb1, GRANT SELECT ON db2.*");
    lhs.clear();
    rhs.clear();
    rhs.grant(AccessType::SELECT, "db2");
    lhs.grant(AccessType::CREATE_TABLE, "db1", "tb1");
    lhs.makeUnion(rhs);
    ASSERT_EQ(lhs.toString(), "GRANT CREATE TABLE ON db1.tb1, GRANT SELECT ON db2.*");
    lhs = {};
    rhs = {};
    lhs.grant(AccessType::SELECT);
    rhs.grant(AccessType::SELECT, "db1", "tb1");