7197350: NPG: jvmtiHeapReferenceCallback receives incorrect reference_kind for system class roots

Fix the iteration over the system classes and report the correct reference kind.

Reviewed-by: coleenp, rbackman

hotspot/src/share/vm/memory/iterator.cpp

@@ -26,6 +26,10 @@
 #include "memory/iterator.hpp"
 #include "oops/oop.inline.hpp"
 
+void KlassToOopClosure::do_klass(Klass* k) {
+  k->oops_do(_oop_closure);
+}
+
 void ObjectToOopClosure::do_object(oop obj) {
   obj->oop_iterate(_cl);
 }