net/http: Add Server.DisableClientPriority field

The DisableClientPriority field is currently still a no-op, and will
only take effect once golang.org/x/net is bundled up into h2_bundle.go
again.

For #75500

Change-Id: I9e2135bed50b7f201aea93467e3f5f5f6c81cb1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/738620
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Nicholas Husin <husin@google.com>

api/next/75500.txt

@@ -0,0 +1 @@
+pkg net/http, type Server struct, DisableClientPriority bool #75500

doc/next/6-stdlib/99-minor/net/http/75500.md

@@ -0,0 +1,4 @@
+HTTP/2 server now accepts client priority signals, as defined in RFC 9218,
+allowing it to prioritize serving HTTP/2 streams with higher priority. If the
+old behavior is preferred, where streams are served in a round-robin manner
+regardless of priority, [Server.DisableClientPriority] can be set to `true`.

src/net/http/server.go

@@ -3074,6 +3074,17 @@ type Server struct {
 	// the default is HTTP/1 only.
 	Protocols *Protocols
 
+	// DisableClientPriority specifies whether client-specified priority, as
+	// specified in RFC 9218, should be respected or not.
+	//
+	// This field only takes effect if using HTTP/2, and if no custom write
+	// scheduler is defined for the HTTP/2 server. Otherwise, this field is a
+	// no-op.
+	//
+	// If set to true, requests will be served in a round-robin manner, without
+	// prioritization.
+	DisableClientPriority bool
+
 	inShutdown atomic.Bool // true when server is in shutdown
 
 	disableKeepAlives atomic.Bool