ocfs2: fix non-auto defrag path not working issue

This fixes three issues on move extents ioctl without auto defrag:

a) In ocfs2_find_victim_alloc_group(), we have to convert bits to block
   first in case of global bitmap.

b) In ocfs2_probe_alloc_group(), when finding enough bits in block
   group bitmap, we have to back off move_len to start pos as well,
   otherwise it may corrupt filesystem.

c) In ocfs2_ioctl_move_extents(), set me_threshold both for non-auto
   and auto defrag paths.  Otherwise it will set move_max_hop to 0 and
   finally cause unexpectedly ENOSPC error.

Currently there are no tools triggering the above issues since
defragfs.ocfs2 enables auto defrag by default.  Tested with manually
changing defragfs.ocfs2 to run non auto defrag path.

Link: https://lkml.kernel.org/r/20230220050526.22020-1-heming.zhao@suse.com
Signed-off-by: Heming Zhao <heming.zhao@suse.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>