Add notifications on configuration and state changes from OpenThread. (#146)

Example state changes that will cause a notification:
- IPv6 address added/removed
- Device state (offline, detached, attached)
- Device role (disabled, detached, child, router, leader)
- Partition ID
- Key Sequence
- Child added/removed

include/openthread-types.h

@@ -206,6 +206,24 @@ typedef struct otLinkModeConfig
     uint8_t mNetworkData : 1;
 } otLinkModeConfig;
 
+/**
+ * This enumeration represents flags that indicate what configuration or state has changed within OpenThread.
+ *
+ */
+enum
+{
+    OT_IP6_ADDRESS_ADDED    = 1 << 0,  ///< IPv6 address was added
+    OT_IP6_ADDRESS_REMOVED  = 1 << 1,  ///< IPv6 address was removed
+
+    OT_NET_STATE            = 1 << 2,  ///< Device state (offline, detached, attached) changed
+    OT_NET_ROLE             = 1 << 3,  ///< Device role (disabled, detached, child, router, leader) changed
+    OT_NET_PARTITION_ID     = 1 << 4,  ///< Partition ID changed
+    OT_NET_KEY_SEQUENCE     = 1 << 5,  ///< Thread Key Sequence changed
+
+    OT_THREAD_CHILD_ADDED   = 1 << 6,  ///< Child was added
+    OT_THREAD_CHILD_REMOVED = 1 << 7   ///< Child was removed
+};
+
 /**
  * @}
  */

include/openthread.h

@@ -457,6 +457,24 @@ ThreadError otAddUnicastAddress(otNetifAddress *aAddress);
  */
 ThreadError otRemoveUnicastAddress(otNetifAddress *aAddress);
 
+/**
+ * This function pointer is called to notify certain configuration or state changes within OpenThread.
+ *
+ * @param[in]  aFlags    A bit-field indicating specific state that has changed.
+ * @param[in]  aContext  A pointer to application-specific context.
+ *
+ */
+typedef void (*otStateChangedCallback)(uint32_t aFlags, void *aContext);
+
+/**
+ * This function registers a callback to indicate when certain configuration or state changes within OpenThread.
+ *
+ * @param[in]  aCallback  A pointer to a function that is called with certain configuration or state changes.
+ * @param[in]  aContext   A pointer to application-specific context.
+ *
+ */
+void otSetStateChangedCallback(otStateChangedCallback aCallback, void *aContext);
+
 /**
  * @}
  */