ygot doesn't support a union with multiple enums

[upavlo]

When generating a proto message, if more than one enum is defined within a union then ygot will pick whatever the first enum that is declared in the schema, instead of listing them all within oneof message.

Consider example:

container bar {
    leaf my-mode {
        type union {
            type string;
            type enumeration {
                enum short;
                enum long;
                enum wide;
            }
            type enumeration {
                enum red;
                enum green;
                enum blue;
            }
        }
    }
}

When this is given to ygot the oneof message will contain one string and one enum (the first one).

In the real openconfig schema the following leafs have a union type with multiple enums:

• /openconfig-network-instance/network-instances/network-instance/protocols/protocol/isis/interfaces/interface/levels/level/afi-safi/af/segment-routing/adjacency-sids/adjacency-sid/state/sid-id
• /openconfig-network-instance/network-instances/network-instance/protocols/protocol/isis/interfaces/interface/levels/level/afi-safi/af/segment-routing/adjacency-sids/adjacency-sid/config/sid-id

Interestingly, if union contains multiple identifyrefs then each one will have an entry in the oneof message.

[wenovus]

Confirmed that this an issue with the given OC paths. sid-id's DYNAMIC enum value is ungenerated.

[wenovus]

Fixing https://github.com/openconfig/goyang/issues/131 is a prerequisite.