LU-14004 llite: default lsm update may memory leak

LU-14004 llite: default lsm update may memory leak

ll_update_default_lsm_md() should check whether lli_default_lsm_md
is set before setting it to the data from lustre_md, and if it's set,
release the old data to avoid memory leak.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I9c8434c5d62f9fb751788031d6769fd49427c371
Reviewed-on: https://review.whamcloud.com/40103
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>