[protobuf] update flow.pb.go with protobuf 3.0.0 beta 2
[protobuf] update flow.pb.go with protobuf 3.0.0 beta 2

Update the generated protobuf file, from the new release protobuf 3.0.0 beta 2.

Change-Id: I41682e7fac31c3fada0e061963c991fbfe800834

fdebonneval/skydive,fdebonneval/skydive,fdebonneval/skydive