Add net.mtu_ipv6 CVar.

Wires up to the new MaximumTransmissionUnitV6 configuration in Lidgren. Default is that of Lidgren.

RELEASE-NOTES.md

@@ -42,6 +42,7 @@ END TEMPLATE-->
 * Made a new `IMetricsManager` interface with an `UpdateMetrics` event that can be used to update Prometheus metrics whenever they are scraped.
   * Also added a `metrics.update_interval` CVar to go along with this, when metrics are scraped without usage of Prometheus directly.
 * IoC now contains an `IMeterFactory` implementation that you can use to instantiate metric meters.
+* `net.mtu_ipv6` CVar allows specifying a different MTU value for IPv6.
 
 ### Bugfixes
 

Robust.Shared/CVars.cs

@@ -65,16 +65,26 @@ namespace Robust.Shared
             CVarDef.Create("net.pool_size", 512, CVar.CLIENT | CVar.SERVER);
 
         /// <summary>
-        /// Maximum UDP payload size to send.
+        /// Maximum UDP payload size to send by default, for IPv4.
         /// </summary>
         /// <seealso cref="NetMtuExpand"/>
+        /// <seealso cref="NetMtuIpv6"/>
         public static readonly CVarDef<int> NetMtu =
             CVarDef.Create("net.mtu", 900, CVar.ARCHIVE);
 
+        /// <summary>
+        /// Maximum UDP payload size to send by default, for IPv6.
+        /// </summary>
+        /// <seealso cref="NetMtu"/>
+        /// <seealso cref="NetMtuExpand"/>
+        public static readonly CVarDef<int> NetMtuIpv6 =
+            CVarDef.Create("net.mtu_ipv6", NetPeerConfiguration.kDefaultMTUV6, CVar.ARCHIVE);
+
         /// <summary>
         /// If set, automatically try to detect MTU above <see cref="NetMtu"/>.
         /// </summary>
         /// <seealso cref="NetMtu"/>
+        /// <seealso cref="NetMtuIpv6"/>
         /// <seealso cref="NetMtuExpandFrequency"/>
         /// <seealso cref="NetMtuExpandFailAttempts"/>
         public static readonly CVarDef<bool> NetMtuExpand =

Robust.Shared/Network/NetManager.cs

@@ -619,6 +619,7 @@ namespace Robust.Shared.Network
 
             // MTU stuff.
             netConfig.MaximumTransmissionUnit = _config.GetCVar(CVars.NetMtu);
+            netConfig.MaximumTransmissionUnitV6 = _config.GetCVar(CVars.NetMtuIpv6);
             netConfig.AutoExpandMTU = _config.GetCVar(CVars.NetMtuExpand);
             netConfig.ExpandMTUFrequency = _config.GetCVar(CVars.NetMtuExpandFrequency);
             netConfig.ExpandMTUFailAttempts = _config.GetCVar(CVars.NetMtuExpandFailAttempts);