shutdown: Destroy kernel last

Currently the shutdown function resets the kernel before the
chainman and scheduler. Invert this order by resetting the kernel
last, since they might rely on the kernel.

src/init.cpp

@@ -341,11 +341,11 @@ void Shutdown(NodeContext& node)
     node.chain_clients.clear();
     UnregisterAllValidationInterfaces();
     GetMainSignals().UnregisterBackgroundSignalScheduler();
-    node.kernel.reset();
     node.mempool.reset();
     node.fee_estimator.reset();
     node.chainman.reset();
     node.scheduler.reset();
+    node.kernel.reset();
 
     try {
         if (!fs::remove(GetPidFile(*node.args))) {