Fix ASharedMemory doxygen formatting, add availability.

Bug: N/A
Test: ran doxygen locally
Change-Id: Ia9924a719a79852a809d4c9989960e19931c4f5e
diff --git a/include/android/sharedmem_jni.h b/include/android/sharedmem_jni.h
index 85ac78f..2af3955 100644
--- a/include/android/sharedmem_jni.h
+++ b/include/android/sharedmem_jni.h
@@ -21,6 +21,7 @@
 
 /**
  * @file sharedmem_jni.h
+ * @brief Shared memory buffers that can be shared across process.
  */
 
 #ifndef ANDROID_SHARED_MEMORY_JNI_H
@@ -46,10 +47,6 @@
  *   - DO NOT CHANGE THE LAYOUT OR SIZE OF STRUCTURES
  */
 
-/**
- * Structures and functions for a shared memory buffer that can be shared across process.
- */
-
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -64,6 +61,8 @@
  *
  * Use close() to release the shared memory region.
  *
+ * Available since API level 27.
+ *
  * \param env The JNIEnv* pointer
  * \param sharedMemory The Java android.os.SharedMemory object
  * \return file descriptor that denotes the shared memory; -1 if the shared memory object is