LU-14918 osd: don't declare similar ldiskfs writes twice

LU-14918 osd: don't declare similar ldiskfs writes twice

in some cases (like overstriping) the same operations can be
declared multiple times (new llog records) and this lead to
huge number of credits and performance degradation. we can
avoid this checking for duplicate declarations.
As every declaration would need an allocation, limit the scope
of this checks to transaction likely to be large.

% of "large" transaction in sanity-benchmark, depending on threshold:

  creates < 5 && writes < 5:
  0.58% (mds1) and  2.97% (mds2)

  create < 7 & writes < 7:
  0.58% and 2.4%

  create < 9 & writes  < 9:
  0.6% and 1.85%

  create < 10 & write2 < 10:
  0.0004% and 0.000001%

thus 10 creates or writes is selected as a threshold to enable this
logic.

Lustre-change: https://review.whamcloud.com/45765
Lustre-commit: 9e6225b2e7385cbb7be0474df01075fafc4966d5

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I7c893fe3b95646b4b813b999bc832659dfcf03ad
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53485
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>