Fix documentation for AHardwareBuffer_(to|from)HardwareBuffer.

These functions were not showing up in the NDK documentation due to
missing Doxygen commands.

Bug: https://github.com/android-ndk/ndk/issues/706
Bug: 132738639
Test: N/A, documentation-only fix
Change-Id: I329f79da251e62b5f4f05feb7ce837c728e2cb32
diff --git a/include/android/hardware_buffer_jni.h b/include/android/hardware_buffer_jni.h
index 7c4be24..aedf369 100644
--- a/include/android/hardware_buffer_jni.h
+++ b/include/android/hardware_buffer_jni.h
@@ -15,7 +15,13 @@
  */
 
 /**
+ * @addtogroup AHardwareBuffer
+ * @{
+ */
+
+/**
  * @file hardware_buffer_jni.h
+ * @brief JNI glue for native hardware buffers.
  */
 
 #ifndef ANDROID_HARDWARE_BUFFER_JNI_H
@@ -30,23 +36,25 @@
 __BEGIN_DECLS
 
 /**
- * Return the AHardwareBuffer associated with a Java HardwareBuffer object,
- * for interacting with it through native code. This method does not acquire any
- * additional reference to the AHardwareBuffer that is returned. To keep the
- * AHardwareBuffer live after the Java HardwareBuffer object got garbage
- * collected, be sure to use AHardwareBuffer_acquire() to acquire an additional
- * reference.
+ * Return the AHardwareBuffer wrapped by a Java HardwareBuffer object.
+ *
+ * This method does not acquire any additional reference to the AHardwareBuffer
+ * that is returned. To keep the AHardwareBuffer live after the Java
+ * HardwareBuffer object got garbage collected, be sure to use AHardwareBuffer_acquire()
+ * to acquire an additional reference.
  */
 AHardwareBuffer* AHardwareBuffer_fromHardwareBuffer(JNIEnv* env,
-        jobject hardwareBufferObj);
+        jobject hardwareBufferObj) __INTRODUCED_IN(26);
 
 /**
  * Return a new Java HardwareBuffer object that wraps the passed native
  * AHardwareBuffer object.
  */
 jobject AHardwareBuffer_toHardwareBuffer(JNIEnv* env,
-        AHardwareBuffer* hardwareBuffer);
+        AHardwareBuffer* hardwareBuffer) __INTRODUCED_IN(26);
 
 __END_DECLS
 
 #endif // ANDROID_HARDWARE_BUFFER_JNI_H
+
+/** @} */