CAIQUM-5731: Rest call /api/datacenter/storage/volumes shows wrong values for qos policy-group extreme-fixed

Issue

The rest call towards AIQUM for a given volume that has extreme-fixed qos policy assigned, shows 0 on the max_throughput_mbps value. 
For example for volume test1 the call:
https://10.216.26.28/api/datacenter/...mes?name=test1
returns:

.......
"qos": {
        "policy": {
          "key": "acf54920-27a0-11ee-8804-005056b1ebbe:type=qos_policy_group,qos_policy_group_uuid=b7189398-e572-48ab-8f69-82cd46580812",
          "uuid": "b7189398-e572-48ab-8f69-82cd46580812",
          "name": "extreme-fixed",
          "_links": {
            "self": {
              "href": "/api/datacenter/storage/qos/policies/acf54920-27a0-11ee-8804-005056b1ebbe:type=qos_policy_group,qos_policy_group_uuid=b7189398-e572-48ab-8f69-82cd46580812"
            }
          },
          "max_throughput_iops": 50000,
          "max_throughput_mbps": 0,
          "min_throughput_iops": 0
.......