devlink: convert snapshot destructor callback to region op

It does not makes sense that two snapshots for a given region would use
different destructors. Simplify snapshot creation by adding
a .destructor op for regions.

This operation will replace the data_destructor for the snapshot
creation, and makes snapshot creation easier.

Noticed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/netdevsim/dev.c

@@ -56,7 +56,7 @@ static ssize_t nsim_dev_take_snapshot_write(struct file *file,
 
 	id = devlink_region_snapshot_id_get(priv_to_devlink(nsim_dev));
 	err = devlink_region_snapshot_create(nsim_dev->dummy_region,
-					     dummy_data, id, kfree);
+					     dummy_data, id);
 	if (err) {
 		pr_err("Failed to create region snapshot\n");
 		kfree(dummy_data);
@@ -342,6 +342,7 @@ static void nsim_devlink_param_load_driverinit_values(struct devlink *devlink)
 
 static const struct devlink_region_ops dummy_region_ops = {
 	.name = "dummy",
+	.destructor = &kfree,
 };
 
 static int nsim_dev_dummy_region_init(struct nsim_dev *nsim_dev,