Be more like a library to support mobile (#247)

tun_windows.go

@@ -18,9 +18,13 @@ type Tun struct {
 	*water.Interface
 }
 
+func newTunFromFd(deviceFd int, cidr *net.IPNet, defaultMTU int, routes []route, unsafeRoutes []route, txQueueLen int) (ifce *Tun, err error) {
+	return nil, fmt.Errorf("newTunFromFd not supported in Windows")
+}
+
 func newTun(deviceName string, cidr *net.IPNet, defaultMTU int, routes []route, unsafeRoutes []route, txQueueLen int) (ifce *Tun, err error) {
 	if len(routes) > 0 {
-		return nil, fmt.Errorf("Route MTU not supported in Windows")
+		return nil, fmt.Errorf("route MTU not supported in Windows")
 	}
 
 	// NOTE: You cannot set the deviceName under Windows, so you must check tun.Device after calling .Activate()