http2: make the Server use the priority write scheduler

make the Server use the priority write scheduler by default,
this way the defaults will be the same on stdlib and x/net.

xref: https://github.com/golang/go/commit/8f36668178d07e6f1b979252c1c68ebe788d14be

Signed-off-by: Antonio Ojea <antonio.ojea.garcia@gmail.com>
Change-Id: Ibeed7a2bb8949d9bc5edb30fc723427f6cc157be
Reviewed-on: https://go-review.googlesource.com/c/net/+/382015
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
diff --git a/http2/server.go b/http2/server.go
index b1c32eb..4bb0d66 100644
--- a/http2/server.go
+++ b/http2/server.go
@@ -400,7 +400,7 @@
 	if s.NewWriteScheduler != nil {
 		sc.writeSched = s.NewWriteScheduler()
 	} else {
-		sc.writeSched = NewRandomWriteScheduler()
+		sc.writeSched = NewPriorityWriteScheduler(nil)
 	}
 
 	// These start at the RFC-specified defaults. If there is a higher