wgengine/wgint: add shady temporary package to get at wireguard internals

For #5451

Change-Id: I43482289e323ba9142a446d551ab7a94a467c43a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/wgint/wgint_test.go

@@ -0,0 +1,24 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package wgint
+
+import (
+	"testing"
+
+	"golang.zx2c4.com/wireguard/device"
+)
+
+func TestPeerStats(t *testing.T) {
+	peer := new(device.Peer)
+	if got := PeerLastHandshakeNano(peer); got != 0 {
+		t.Errorf("PeerLastHandshakeNano = %v, want 0", got)
+	}
+	if got := PeerRxBytes(peer); got != 0 {
+		t.Errorf("PeerRxBytes = %v, want 0", got)
+	}
+	if got := PeerTxBytes(peer); got != 0 {
+		t.Errorf("PeerTxBytes = %v, want 0", got)
+	}
+}