vmm: api: Match VhostUserBlkConfig defaults between CLI and HTTP API

In order to let the CLI and the HTTP API behave the same regarding the
VhostUserBlkConfig structure, this patch defines some default values
for num_queues, queue_size and wce.

num_queues is 1, queue_size is 128 and wce is true.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -391,19 +391,19 @@ components:
     VhostUserBlkConfig:
       required:
       - sock
-      - num_queues
-      - queue_size
-      - wce
       type: object
       properties:
         sock:
           type: string
         num_queues:
           type: integer
+          default: 1
         queue_size:
           type: integer
+          default: 128
         wce:
           type: boolean
+          default: true
 
     VsockConfig:
       required: