message: fix tag in update and sum2 messages
diff: @@ -516,7 +516,7 @@ impl Message {
  participant_pk,
  coordinator_pk,
  is_multipart: false,
  - tag: Tag::Sum,
  + tag: Tag::Sum2,
  payload: message.into(),
  }
  }
  @@ -533,7 +533,7 @@ impl Message {
  participant_pk,
  coordinator_pk,
  is_multipart: false,
  - tag: Tag::Sum,
  + tag: Tag::Update,
  payload: message.into(),
  }
  }
  