message: Add a check that set_state always results in a state change
  It does now, but let's make sure it stays that way.
diff: @@ -356,6 +356,10 @@ impl RecvStream {
  }
  fn set_state(&mut self, new_state: RecvStreamState) {
  + assert_ne!(
  + mem::discriminant(&self.state),
  + mem::discriminant(&new_state)
  + );
  qtrace!(
  "RecvStream {} state {} -> {}",
  self.stream_id.as_u64(),
  