Make sure to test IPv6

src/Tgstation.Server.Host/Components/InstanceManager.cs

@@ -481,7 +481,7 @@ namespace Tgstation.Server.Host.Components
 
 			// This runs before the real socket is opened, ensures we don't perform reattaches unless we're fairly certain the bind won't fail
 			// If it does fail, DD will be killed.
-			SocketExtensions.BindTest(serverPortProvider.HttpApiPort);
+			SocketExtensions.BindTest(serverPortProvider.HttpApiPort, true);
 		}
 
 		/// <inheritdoc />

src/Tgstation.Server.Host/Components/Session/SessionControllerFactory.cs

@@ -120,7 +120,7 @@ namespace Tgstation.Server.Host.Components.Session
 		{
 			try
 			{
-				SocketExtensions.BindTest(port);
+				SocketExtensions.BindTest(port, false);
 			}
 			catch (SocketException ex) when (ex.SocketErrorCode == SocketError.AddressAlreadyInUse)
 			{

src/Tgstation.Server.Host/Extensions/SocketExtensions.cs

@@ -12,12 +12,21 @@ namespace Tgstation.Server.Host.Extensions
 		/// Attempt to exclusively bind to a given <paramref name="port"/>.
 		/// </summary>
 		/// <param name="port">The port number to bind to.</param>
-		public static void BindTest(ushort port)
+		/// <param name="includeIPv6">If IPV6 should be tested as well.</param>
+		public static void BindTest(ushort port, bool includeIPv6)
 		{
 			using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
 			socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ExclusiveAddressUse, true);
 			socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, false);
-			socket.Bind(new IPEndPoint(IPAddress.Any, port));
+			if (includeIPv6)
+				socket.DualMode = true;
+
+			socket.Bind(
+				new IPEndPoint(
+					includeIPv6
+						? IPAddress.IPv6Any
+						: IPAddress.Any,
+					port));
 		}
 	}
 }