conn: implement RIO for fast Windows UDP sockets

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/queueconstants_default.go

@@ -1,4 +1,4 @@
-// +build !android,!ios
+// +build !android,!ios,!windows
 
 /* SPDX-License-Identifier: MIT
  *

device/queueconstants_windows.go

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package device
+
+const (
+	QueueStagedSize            = 128
+	QueueOutboundSize          = 1024
+	QueueInboundSize           = 1024
+	QueueHandshakeSize         = 1024
+	MaxSegmentSize             = 2048 - 32 // largest possible UDP datagram
+	PreallocatedBuffersPerPool = 0         // Disable and allow for infinite memory growth
+)