message: perf(http2): improve Body::is_end_stream detection for http2
diff: @@ -318,7 +318,7 @@ impl Payload for Body {
  fn is_end_stream(&self) -> bool {
  match self.kind {
  Kind::Chan { .. } => false,
  - Kind::H2(..) => false,
  + Kind::H2(ref h2) => h2.is_end_stream(),
  Kind::Wrapped(..) => false,
  Kind::Once(ref val) => val.is_none(),
  Kind::Empty => true
  