nvme: add 'kato' sysfs attribute

Add a 'kato' controller sysfs attribute to display the current
keep-alive timeout value (if any). This allows userspace to identify
persistent discovery controllers, as these will have a non-zero
KATO value.
Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -3172,6 +3172,7 @@ nvme_show_int_function(cntlid);
 nvme_show_int_function(numa_node);
 nvme_show_int_function(queue_count);
 nvme_show_int_function(sqsize);
+nvme_show_int_function(kato);
 
 static ssize_t nvme_sysfs_delete(struct device *dev,
 				struct device_attribute *attr, const char *buf,
@@ -3369,6 +3370,7 @@ static struct attribute *nvme_dev_attrs[] = {
 	&dev_attr_ctrl_loss_tmo.attr,
 	&dev_attr_reconnect_delay.attr,
 	&dev_attr_fast_io_fail_tmo.attr,
+	&dev_attr_kato.attr,
 	NULL
 };