relocate to VPN menu

fix #30

root/usr/share/luci/menu.d/luci-app-tailscale.json

@@ -1,5 +1,5 @@
 {
-	"admin/services/tailscale": {
+	"admin/vpn/tailscale": {
 		"title": "Tailscale",
 		"order": 90,
 		"action": {
@@ -10,7 +10,7 @@
 			"uci": { "tailscale": true }
 		}
 	},
-	"admin/services/tailscale/setting": {
+	"admin/vpn/tailscale/setting": {
 		"title": "Global Settings",
 		"order": 10,
 		"action": {
@@ -18,7 +18,7 @@
 			"path": "tailscale/setting"
 		}
 	},
-	"admin/services/tailscale/interface": {
+	"admin/vpn/tailscale/interface": {
 		"title": "Interface Info",
 		"order": 20,
 		"action": {
@@ -26,7 +26,7 @@
 			"path": "tailscale/interface"
 		}
 	},
-	"admin/services/tailscale/log": {
+	"admin/vpn/tailscale/log": {
 		"title": "Logs",
 		"order": 30,
 		"action": {