call volume_rollback_is_possible from PVE::Storage::volume_snapshot_rollback

That way it is automatically called for all plungins.

PVE/Storage/ZFSPlugin.pm

@@ -310,9 +310,6 @@ sub volume_resize {
 sub volume_snapshot_rollback {
     my ($class, $scfg, $storeid, $volname, $snap) = @_;
 
-    # abort rollback if snapshot is not the latest
-    $class->volume_rollback_is_possible($scfg, $storeid, $volname, $snap);
-    
     $class->zfs_delete_lu($scfg, $volname);
 
     $class->zfs_request($class, $scfg, undef, 'rollback', "$scfg->{pool}/$volname\@$snap");