reverting UserDefinedStats use of DSSum
reverting UserDefinedStats use of DSSum

- in preparation for changing the DSSum API.
Partial-Bug: 1600376

Change-Id: Ib4ed31368a2b83ee43af7d66f3a75be33fb9f367

tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller