libbinder: emphasize kernel state objs

ProcessState/IPCThreadState objects are kernel objects,
and they are not used for RPC binder. Though, because
they have general names (they were created before we
co-opted userspace binder on top of sockets), this
deserves a comment explanation.

Bug: 237245600
Test: N/A
Change-Id: I914fa0578bac81fa131c8a1c1e28a99ca6b781bc
diff --git a/libs/binder/include/binder/IPCThreadState.h b/libs/binder/include/binder/IPCThreadState.h
index cd6a274..8ce3bc9 100644
--- a/libs/binder/include/binder/IPCThreadState.h
+++ b/libs/binder/include/binder/IPCThreadState.h
@@ -28,6 +28,10 @@
 // ---------------------------------------------------------------------------
 namespace android {
 
+/**
+ * Kernel binder thread state. All operations here refer to kernel binder. This
+ * object is allocated per-thread.
+ */
 class IPCThreadState
 {
 public:
diff --git a/libs/binder/include/binder/ProcessState.h b/libs/binder/include/binder/ProcessState.h
index e17a76c..882dfbf 100644
--- a/libs/binder/include/binder/ProcessState.h
+++ b/libs/binder/include/binder/ProcessState.h
@@ -29,6 +29,10 @@
 
 class IPCThreadState;
 
+/**
+ * Kernel binder process state. All operations here refer to kernel binder. This
+ * object is allocated per process.
+ */
 class ProcessState : public virtual RefBase {
 public:
     static sp<ProcessState> self();