zpool_get_vdev_prop_value: show missing vdev userprops

If a vdev userprop is not found, present it as value '-', default
source, so it matches the output from pool userprops.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes #16887

Author: robn

lib/libzfs/libzfs_pool.c

@@ -5342,7 +5342,8 @@ zpool_get_vdev_prop_value(nvlist_t *nvprop, vdev_prop_t prop, char *prop_name,
 			strval = fnvlist_lookup_string(nv, ZPROP_VALUE);
 		} else {
 			/* user prop not found */
-			return (-1);
+			src = ZPROP_SRC_DEFAULT;
+			strval = "-";
 		}
 		(void) strlcpy(buf, strval, len);
 		if (srctype)