LU-8370 dne: error in spliting update records

LU-8370 dne: error in spliting update records

sub_updates_write() needs to split update records if it exceeds
llog_chunk_size, current code is not accurate in offset
calculation, now it's changed to use the same set of functions to
estimate and set update llog size.

Besides, the padding size of each split llog should >=
LLOG_MIN_REC_SIZE, or exactly matches llog chunk size, otherwise
llog_osd_pad() will LASSERT.

Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Change-Id: I061c7808b26ce98967858bbed88b9e5180d88289
Reviewed-on: http://review.whamcloud.com/21334
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>