net/http: updated bundled copy of x/net/http2

Updates to x/net/http2 git rev c24de9d5

Change-Id: I3d929ae38dca1a93e9a262d4eaaafee1d36fa839
Reviewed-on: https://go-review.googlesource.com/17896Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/vendor/golang.org/x/net/http2/hpack/hpack.go

@@ -102,6 +102,13 @@ func (d *Decoder) SetMaxStringLength(n int) {
 	d.maxStrLen = n
 }
 
+// SetEmitFunc changes the callback used when new header fields
+// are decoded.
+// It must be non-nil. It does not affect EmitEnabled.
+func (d *Decoder) SetEmitFunc(emitFunc func(f HeaderField)) {
+	d.emit = emitFunc
+}
+
 // SetEmitEnabled controls whether the emitFunc provided to NewDecoder
 // should be called. The default is true.
 //