Describe the feature request
In virtual_service.proto we set grpc_status as string (and it's hide_from_docs for now). It's a little confused why it's string rather than int32. Maybe a int32 in 0-16 range is more efficient.

And envoy support grpc_status in v3, see: PR and proto, and it set grpc_status as a int32.

BTW don't know whether it's some compatibility issues if we do this change.

Describe alternatives you've considered

1. Change grpc_status from string to int32 in fault abort protos.
2. Implement this feature after we move to envoy v3.

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