vmm: Support vhost-user-net via "--net"

Add a socket and vhost_user parameter to this option so that the same
configuration option can be used for both virtio-net and vhost-user-net.
For now it is necessary to specify both vhost_user and socket parameters
as auto activation is not yet implemented. The original command line
parameter is still supported for now.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

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

@@ -307,6 +307,11 @@ components:
         queue_size:
           type: integer
           default: 256
+        vhost_user:
+          type: boolean
+          default: false
+        vhost_socket:
+          type: string
 
     RngConfig:
       required: