fix: Clearing TransportEvent delegate event when failing to host. [MTT-3421] (#1938)

* fix: Clearing TransportEvent delegate event when failing to host. Fixes an issue where hosting again after hosting with invalid params would result in doubly-delivered messages followed by time-out

* fix: Clearing TransportEvent delegate (changelog)

Author: jeffreyrainy

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
+### Fixed
+
+- Fixed: Hosting again after failing to host now works correctly
+
 ## [1.0.0-pre.8] - 2022-04-27
 
 ### Changed

com.unity.netcode.gameobjects/Runtime/Core/NetworkManager.cs

@@ -1175,6 +1175,8 @@ public void Shutdown(bool discardMessageQueue = false)
                 m_ShuttingDown = true;
                 m_StopProcessingMessages = discardMessageQueue;
             }
+
+            NetworkConfig.NetworkTransport.OnTransportEvent -= HandleRawTransportPoll;
         }
 
         internal void ShutdownInternal()