Add VS support for setting stats via redis DB channel (sonic-net#366)

* Add VS support for setting stats via redis DB channel

* Remove SET description

Author: kcudnik

vslib/inc/sai_vs.h

@@ -41,6 +41,13 @@ extern "C" {
  */
 #define SAI_VS_UNITTEST_SET_RO_OP   "set_ro"
 
+/**
+ * @def SAI_VS_UNITTEST_SET_STATS
+ *
+ * Notification operation for "SET" stats on specific object.
+ */
+#define SAI_VS_UNITTEST_SET_STATS_OP      "set_stats"
+
 /**
  * @def SAI_VS_UNITTEST_ENABLE
  *