fix dns leak (#7110)

v2rayN/ServiceLib/Models/V2rayConfig.cs

@@ -210,6 +210,7 @@ public class DnsServer4Ray
 {
     public string? address { get; set; }
     public List<string>? domains { get; set; }
+    public bool? skipFallback { get; set; }
 }
 
 public class Routing4Ray

v2rayN/ServiceLib/Sample/dns_v2ray_normal

@@ -15,6 +15,7 @@
     },
     {
       "address": "223.5.5.5",
+      "skipFallback": true,
       "domains": [
         "geosite:cn"
       ],

v2rayN/ServiceLib/Services/CoreConfig/CoreConfigV2rayService.cs

@@ -1185,6 +1185,7 @@ public class CoreConfigV2rayService
                 var dnsServer = new DnsServer4Ray()
                 {
                     address = string.IsNullOrEmpty(dNSItem?.DomainDNSAddress) ? Global.DomainDNSAddress.FirstOrDefault() : dNSItem?.DomainDNSAddress,
+                    skipFallback = true,
                     domains = [node.Address]
                 };
                 servers.AsArray().Add(JsonUtils.SerializeToNode(dnsServer));