Kernel: Switch singletons to use new Singleton class

Fixes #3226

Kernel/Net/LoopbackAdapter.cpp

@@ -25,15 +25,15 @@
  */
 
 #include <Kernel/Net/LoopbackAdapter.h>
+#include <Kernel/Singleton.h>
 
 namespace Kernel {
 
+static auto s_loopback = make_singleton<LoopbackAdapter>();
+
 LoopbackAdapter& LoopbackAdapter::the()
 {
-    static LoopbackAdapter* the;
-    if (!the)
-        the = new LoopbackAdapter;
-    return *the;
+    return *s_loopback;
 }
 
 LoopbackAdapter::LoopbackAdapter()