Fix memory leak of OVSDB

Change-Id: Iebe692eda2af68400f19b4de40db5cd4afba802e
diff --git a/protocols/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java b/protocols/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
index 862d70c..3f8ec1c 100644
--- a/protocols/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
+++ b/protocols/ovsdb/api/src/main/java/org/onosproject/ovsdb/controller/driver/DefaultOvsdbClient.java
@@ -1387,6 +1387,9 @@
         }
         String methodName = requestMethod.get(requestId);
         sf.set(FromJsonUtil.jsonResultParser(response, methodName));
+
+        requestResult.remove(requestId);
+        requestMethod.remove(requestId);
     }
 
     @Override