enum directive ignored in params list
```yaml
type:
  # ...
  payload:
    params:
    - id: rec_type
      enum: rec_types
      type: u1
    seq:
    - id: data
      #process: xor(0)
      type:
        cases:
          rec_types::type_1: type_1
          rec_types::type_2: type_2
        switch-on: rec_type
```
Produces errors, such as:
```
/types/payload/seq/0/type/cases/EnumByLabel(identifier(rec_types),identifier(type_2)): can't compare Int1Type(false) and EnumType(List(rec_types),CalcIntType)
```
(See [Lobby discussion](https://gitter.im/kaitai_struct/Lobby?at=5acbb331080a38505313c74b).)