vhost: introduce new VhostOps vhost_set_config_call

This patch introduces new VhostOps vhost_set_config_call. This function allows the
vhost to set the event fd to kernel

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20211104164827.21911-5-lulu@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/hw/virtio/vhost-backend.h

@@ -126,6 +126,8 @@ typedef int (*vhost_get_device_id_op)(struct vhost_dev *dev, uint32_t *dev_id);
 
 typedef bool (*vhost_force_iommu_op)(struct vhost_dev *dev);
 
+typedef int (*vhost_set_config_call_op)(struct vhost_dev *dev,
+                                       int fd);
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_backend_init vhost_backend_init;
@@ -171,6 +173,7 @@ typedef struct VhostOps {
     vhost_vq_get_addr_op  vhost_vq_get_addr;
     vhost_get_device_id_op vhost_get_device_id;
     vhost_force_iommu_op vhost_force_iommu;
+    vhost_set_config_call_op vhost_set_config_call;
 } VhostOps;
 
 int vhost_backend_update_device_iotlb(struct vhost_dev *dev,