net/netns: add windows support.

Also remove rebinding logic from the windows router. Magicsock will
instead rebind based on link change signals.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/router/router_windows.go

@@ -49,13 +49,10 @@ func newUserspaceRouter(logf logger.Logf, wgdev *device.Device, tundev tun.Devic
 }
 
 func (r *winRouter) Up() error {
-	// MonitorDefaultRoutes handles making sure our wireguard UDP
-	// traffic goes through the old route, not recursively through the VPN.
-
 	r.removeFirewallAcceptRule()
 
 	var err error
-	r.routeChangeCallback, err = monitorDefaultRoutes(r.wgdev, true, r.nativeTun)
+	r.routeChangeCallback, err = monitorDefaultRoutes(r.nativeTun)
 	if err != nil {
 		log.Fatalf("MonitorDefaultRoutes: %v", err)
 	}
@@ -116,6 +113,7 @@ func (r *winRouter) Close() error {
 	if r.routeChangeCallback != nil {
 		r.routeChangeCallback.Unregister()
 	}
+
 	return nil
 }