To compile the proto buffers definition you need to install version latest version of protocol buffers.
See https://github.com/google/protobuf/releases for releases and https://developers.google.com/protocol-buffers/ for documentation.
Install the necessary go packages:
go get -a github.com/golang/protobuf/protoc-gen-go go get -u google.golang.org/grpc
To generate code run in this directory:
go generate ./...
Or use protoc directly:
protoc --go_out=plugins=grpc:. diffservice.proto