LU-18639 dne: a correct check for dir split

LU-18639 dne: a correct check for dir split

Use the actual dir stripe count while performing
a dir split sanity check in lod_dir_declare_dir_split().

Fix lod_object_lock() to work with a striped dir with
only one stripe correctly.

Improve sanity test_230p by adding a dir split right
after the dir merges.

Also fix a typo in lustre/doc/lfs-migrate.1 .

Fixes: 2e2b16c28b ("LU-11025 dne: support directory restripe")
Fixes: 392f558f40 ("LU-17810 dne: dir restripe without fixed hash flag")
HPE-bug-id: LUS-12701
Test-Parameters: envdefinitions=ONLY=230p fstype=ldiskfs mdtcount=2 mdscount=2 testlist=sanity
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Change-Id: I8d8501fd09f89d03ccb1ea92a8562326110ecc24
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57784
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>