Fix UDP plugin server not accepting packets

AssettoServer/Utils/SocketAddressExtensions.cs

@@ -1,10 +1,14 @@
 using System;
 using System.Net;
+using System.Reflection;
 
 namespace AssettoServer.Utils;
 
 public static class SocketAddressExtensions
 {
+    private static readonly GetIPv4AddressMethod GetIPv4AddressDelegate;
+    private delegate uint GetIPv4AddressMethod(ReadOnlySpan<byte> buffer);
+
     public static SocketAddress Clone(this SocketAddress address)
     {
         var clone = new SocketAddress(address.Family, address.Size);
@@ -14,7 +18,19 @@ public static SocketAddress Clone(this SocketAddress address)
 
     public static bool IpEquals(this SocketAddress address, SocketAddress other)
     {
-        // This works for IPv4 only. First two bytes = port, next 4 bytes = address
-        return address.Buffer.Span[2..6].SequenceEqual(other.Buffer.Span[2..6]);
+        return address.GetIPv4Address() == other.GetIPv4Address();
+    }
+
+    public static uint GetIPv4Address(this SocketAddress address)
+    {
+        return GetIPv4AddressDelegate(address.Buffer.Span);
+    }
+
+    static SocketAddressExtensions()
+    {
+        GetIPv4AddressDelegate = Assembly.GetAssembly(typeof(SocketAddress))!
+            .GetType("System.Net.SocketAddressPal")!
+            .GetMethod("GetIPv4Address", BindingFlags.Public | BindingFlags.Static)!
+            .CreateDelegate<GetIPv4AddressMethod>();
     }
 }