[kernel] add RT_IPC_CMD_GET_STATE definition

include/rtdef.h

@@ -775,6 +775,7 @@ typedef struct rt_thread *rt_thread_t;
 
 #define RT_IPC_CMD_UNKNOWN              0x00            /**< unknown IPC command */
 #define RT_IPC_CMD_RESET                0x01            /**< reset IPC object */
+#define RT_IPC_CMD_GET_STATE            0x02            /**< get the state of IPC object */
 
 #define RT_WAITING_FOREVER              -1              /**< Block forever until get resource. */
 #define RT_WAITING_NO                   0               /**< Non-block. */