LU-10220 mdd: fix buf alloc in mdd_changelog_data_store_by_fid

LU-10220 mdd: fix buf alloc in mdd_changelog_data_store_by_fid

Fix allocation of mti_big_buf by call to lu_buf_check_and_alloc()
in mdd_changelog_data_store_by_fid().
reclen must take the header size of struct llog_changelog_rec into
account.

Maybe no memory corruptions were seen before because the buffer size
allocated in a previous call to mdd_declare_changelog_store() was
covering the need. But audit will add more information in changelog
records, provoking memory corruptions without this fix.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Id0a06c412b54c0ae12c15d53f3e166e3e5d9ed68
Reviewed-on: https://review.whamcloud.com/30014
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>