LU-6602 llog: increase update llog chunk size

LU-6602 llog: increase update llog chunk size

Increase DNE update llog chunk size from 8KB to 32KB, so
one cross-MDT operation can includes more update records,
and it can create striped directory with more stripe count.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I01d1435f1249c3048ac0a412bdb53f710e6e98b3
Reviewed-on: http://review.whamcloud.com/15161
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>