[release-branch.go1.7] net/http: update bundled http2

Updates bundled http2 for x/net/http2 git rev 8d4d01f0 for:

[release-branch.go1.7] http2: don't sniff first Request.Body byte in Transport until we have a conn
https://golang.org/cl/29074

Fixes #17071

Change-Id: I37fef5c2c0fdf499545f9af08abd5f9edb2da4c0
Reviewed-on: https://go-review.googlesource.com/29111
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>

src/net/http/h2_bundle.go

 // Code generated by golang.org/x/tools/cmd/bundle.
-//go:generate bundle -o h2_bundle.go -prefix http2 golang.org/x/net/http2
+//go:generate bundle -o h2_bundle.go -prefix http2 -underscore golang.org/x/net/http2
 
 // Package http2 implements the HTTP/2 protocol.
 //
@@ -5486,9 +5486,6 @@ func (cc *http2ClientConn) RoundTrip(req *Request) (*Response, error) {
 	}
 	hasTrailers := trailers != ""
 
-	body, contentLen := http2bodyAndLength(req)
-	hasBody := body != nil
-
 	cc.mu.Lock()
 	cc.lastActive = time.Now()
 	if cc.closed || !cc.canTakeNewRequestLocked() {
@@ -5496,6 +5493,9 @@ func (cc *http2ClientConn) RoundTrip(req *Request) (*Response, error) {
 		return nil, http2errClientConnUnusable
 	}
 
+	body, contentLen := http2bodyAndLength(req)
+	hasBody := body != nil
+
 	// TODO(bradfitz): this is a copy of the logic in net/http. Unify somewhere?
 	var requestedGzip bool
 	if !cc.t.disableCompression() &&