zfs: list zvol: limit recursion depth to 1

To be correct in all cases, it's still necessary to filter by "pool"
in zfs_parse_zvol_list(), because $scfg->{pool} could be e.g.
'foo/vm-123-disk-0' which looks like an image name and would pass the
other "should skip"-checks in zfs_parse_zvol_list().

No change in the result of zfs_list_zvol() is intended.

Suggested-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

PVE/Storage/ZFSPoolPlugin.pm

@@ -377,9 +377,12 @@ sub zfs_list_zvol {
 	'name,volsize,origin,type,refquota',
 	'-t',
 	'volume,filesystem',
-	'-Hrp',
+	'-d1',
+	'-Hp',
 	$scfg->{pool},
     );
+    # It's still required to have zfs_parse_zvol_list filter by pool, because -d1 lists
+    # $scfg->{pool} too and while unlikely, it could be named to be mistaken for a volume.
     my $zvols = zfs_parse_zvol_list($text, $scfg->{pool});
     return {} if !$zvols;