Dynamic Max Children (#462)

* Add support for dynamically adjusting the maximum number of allowed children.
* Update cli to support max number of children.

include/openthread.h

@@ -371,6 +371,26 @@ uint8_t otGetChannel(void);
  */
 ThreadError otSetChannel(uint8_t aChannel);
 
+/**
+ * Get the maximum number of children currently allowed.
+ *
+ * @returns The maximum number of children currently allowed.
+ *
+ * @sa otSetMaxAllowedChildren
+ */
+uint8_t otGetMaxAllowedChildren(void);
+
+/**
+ * Set the maximum number of children currently allowed.
+ *
+ * @retval  kThreadErrorNone           Successfully set the max.
+ * @retval  kThreadError_InvalidArgs   If @p aMaxChildren is not in the range [1, OPENTHREAD_CONFIG_MAX_CHILDREN].
+ * @retval  kThreadError_InvalidState  If Thread has already been started.
+ *
+ * @sa otGetMaxAllowedChildren
+ */
+ThreadError otSetMaxAllowedChildren(uint8_t aMaxChildren);
+
 /**
  * Get the Thread Child Timeout used when operating in the Child role.
  *