fix: passing NetworkBehaviors in RPC works with IL2PP (#630)

When passing a NetworkBehavior derived class as a parameter, we were generating
invalid IL.  Mono was ok with it, but it caused a problem for IL2PP

fixes #629

Assets/Mirage/Weaver/Readers.cs

@@ -118,9 +118,14 @@ public MethodReference GetReadFunc(TypeReference typeReference, SequencePoint se
 
         private MethodReference GetNetworkBehaviourReader(TypeReference typeReference)
         {
-            MethodReference readFunc = module.ImportReference<NetworkReader>((reader) => reader.ReadNetworkBehaviour());
-            Register(typeReference, readFunc);
-            return readFunc;
+            MethodDefinition readerFunc = GenerateReaderFunction(typeReference);
+            ILProcessor worker = readerFunc.Body.GetILProcessor();
+
+            worker.Append(worker.Create(OpCodes.Ldarg_0));
+            worker.Append(worker.Create<NetworkReader>(OpCodes.Call, (reader) => reader.ReadNetworkBehaviour()));
+            worker.Append(worker.Create(OpCodes.Castclass, typeReference));
+            worker.Append(worker.Create(OpCodes.Ret));
+            return readerFunc;
         }
 
         void RegisterReadFunc(TypeReference typeReference, MethodDefinition newReaderFunc)