net/http: update bundled http2

Updates http2 to x/net/http2 git rev 292b43b for:

    http2: reject incoming HEADERS in Server on half-closed streams
    https://golang.org/cl/111677

Updates #25023

Change-Id: I479ae9b5b899fb0202e6301d02535fb6aeb4997a
Reviewed-on: https://go-review.googlesource.com/122877Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/h2_bundle.go

@@ -5466,6 +5466,13 @@ func (sc *http2serverConn) processHeaders(f *http2MetaHeadersFrame) error {
 			// processing this frame.
 			return nil
 		}
+		// RFC 7540, sec 5.1: If an endpoint receives additional frames, other than
+		// WINDOW_UPDATE, PRIORITY, or RST_STREAM, for a stream that is in
+		// this state, it MUST respond with a stream error (Section 5.4.2) of
+		// type STREAM_CLOSED.
+		if st.state == http2stateHalfClosedRemote {
+			return http2streamError(id, http2ErrCodeStreamClosed)
+		}
 		return st.processTrailerHeaders(f)
 	}