fix tun for darwin

cmd/gost/route.go

@@ -450,6 +450,7 @@ func (r *route) GenRouters() ([]router, error) {
 			cfg := gost.TunConfig{
 				Name:    node.Get("name"),
 				Addr:    node.Get("net"),
+				Peer:    node.Get("peer"),
 				MTU:     node.GetInt("mtu"),
 				Routes:  tunRoutes,
 				Gateway: node.Get("gw"),

tuntap.go

@@ -48,6 +48,7 @@ type IPRoute struct {
 type TunConfig struct {
 	Name    string
 	Addr    string
+	Peer    string // peer addr of point-to-point on MacOS
 	MTU     int
 	Routes  []IPRoute
 	Gateway string

tuntap_darwin.go

@@ -29,7 +29,12 @@ func createTun(cfg TunConfig) (conn net.Conn, itf *net.Interface, err error) {
 		mtu = DefaultMTU
 	}
 
-	cmd := fmt.Sprintf("ifconfig %s inet %s mtu %d up", ifce.Name(), cfg.Addr, mtu)
+	peer := cfg.Peer
+	if peer == "" {
+		peer = ip.String()
+	}
+	cmd := fmt.Sprintf("ifconfig %s inet %s %s mtu %d up",
+		ifce.Name(), cfg.Addr, peer, mtu)
 	log.Log("[tun]", cmd)
 	args := strings.Split(cmd, " ")
 	if er := exec.Command(args[0], args[1:]...).Run(); er != nil {