Show MTU in network debug panel.

Robust.Client/UserInterface/CustomControls/DebugMonitorControls/DebugNetPanel.cs

@@ -90,7 +90,7 @@ namespace Robust.Client.UserInterface.CustomControls.DebugMonitorControls
             contents.TextMemory = FormatHelpers.FormatIntoMem(_textBuffer,
                 $@"UP: {sentBytes / ONE_KIBIBYTE:N} KiB/s, {sentPackets} pckt/s, {LastSentBytes / ONE_KIBIBYTE:N} KiB, {LastSentPackets} pckt
 DOWN: {receivedBytes / ONE_KIBIBYTE:N} KiB/s, {receivedPackets} pckt/s, {LastReceivedBytes / ONE_KIBIBYTE:N} KiB, {LastReceivedPackets} pckt
-PING: {NetManager.ServerChannel?.Ping ?? -1} ms");
+PING: {NetManager.ServerChannel?.Ping ?? -1} ms, MTU: {NetManager.ServerChannel?.CurrentMtu} B");
         }
     }
 }

Robust.Shared/Network/INetChannel.cs

@@ -67,6 +67,13 @@ namespace Robust.Shared.Network
         /// </summary>
         bool IsHandshakeComplete { get; }
 
+        /// <summary>
+        /// Diagnostic indicating the maximum transmission unit being used for this connection.
+        /// </summary>
+        /// <seealso cref="CVars.NetMtu"/>
+        [ViewVariables]
+        public int CurrentMtu { get; }
+
         /// <summary>
         ///     Creates a new NetMessage to be filled up and sent.
         /// </summary>
@@ -94,6 +101,5 @@ namespace Robust.Shared.Network
         /// <param name="reason">Reason why it was disconnected.</param>
         /// <param name="sendBye">If false, we ghost the remote client and don't tell them they got disconnected properly.</param>
         void Disconnect(string reason, bool sendBye);
-
     }
 }

Robust.Shared/Network/NetManager.NetChannel.cs

@@ -51,6 +51,8 @@ namespace Robust.Shared.Network
             // Only used on server, contains the encryption to use for this channel.
             public NetEncryption? Encryption { get; set; }
 
+            [ViewVariables] public int CurrentMtu => _connection.CurrentMTU;
+
             /// <summary>
             ///     Creates a new instance of a NetChannel.
             /// </summary>

Robust.UnitTesting/RobustIntegrationTest.NetManager.cs

@@ -440,6 +440,7 @@ namespace Robust.UnitTesting
                 public NetUserData UserData { get; }
                 // integration tests don't simulate serializer handshake so this is always true.
                 public bool IsHandshakeComplete => true;
+                public int CurrentMtu => 1000; // Arbitrary.
 
                 // TODO: Should this port value make sense?
                 public IPEndPoint RemoteEndPoint { get; } = new(IPAddress.Loopback, 1212);