misc: chore: Move the LDN constants into a SharedConstants class

src/Ryujinx/Utilities/Configuration/ConfigurationState.Model.cs

@@ -1,5 +1,6 @@
 using ARMeilleure;
 using Gommon;
+using Ryujinx.Ava.Utilities.AppLibrary;
 using Ryujinx.Ava.Utilities.Configuration.System;
 using Ryujinx.Ava.Utilities.Configuration.UI;
 using Ryujinx.Common;
@@ -647,6 +648,14 @@ namespace Ryujinx.Ava.Utilities.Configuration
             /// </summary>
             public ReactiveObject<string> LdnServer { get; private set; }
 
+            public string GetLdnServer()
+            {
+                string ldnServer = LdnServer;
+                return string.IsNullOrEmpty(ldnServer) 
+                    ? SharedConstants.DefaultLanPlayHost 
+                    : ldnServer;
+            }
+
             public MultiplayerSection()
             {
                 LanInterfaceId = new ReactiveObject<string>();