control: Make decrease interval optional

The `decrease_interval` configuration attribute should be optional where
it defaults to 0 when not given. A decrease interval of 0 disables the
decrease timer.

Change-Id: Ie88d94edb286870c7b8965a4ee778c89c08cc00e
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/control/json/zone.hpp b/control/json/zone.hpp
index 50d8718..f209b4a 100644
--- a/control/json/zone.hpp
+++ b/control/json/zone.hpp
@@ -369,7 +369,7 @@
     /* Zone's increase delay(in seconds) (OPTIONAL) */
     std::chrono::seconds _incDelay;
 
-    /* Zone's decrease interval(in seconds) */
+    /* Zone's decrease interval(in seconds) (OPTIONAL) */
     std::chrono::seconds _decInterval;
 
     /* The floor target to not go below */
@@ -436,16 +436,6 @@
     void setPowerOnTarget(const json& jsonObj);
 
     /**
-     * @brief Parse and set the zone's decrease interval(in seconds)
-     *
-     * @param[in] jsonObj - JSON object for the zone
-     *
-     * Sets the decrease interval(in seconds) for the zone from the JSON
-     * configuration object
-     */
-    void setDecInterval(const json& jsonObj);
-
-    /**
      * @brief Parse and set the interfaces served by the zone(OPTIONAL)
      *
      * @param[in] jsonObj - JSON object for the zone