LU-15168 osd: use large allocation for idc cache

LU-15168 osd: use large allocation for idc cache

as in some cases (e.g. ofd precreate) the cache can grow to dozens
of kilobytes (sizeof(struct idc_map_cache)=40 * 1024).

Lustre-commit: a3aa2eefd3d4708ce7094ed644c30b784c39eb2c
Lustre-change: https://review.whamcloud.com/45382

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Id9e0996a7a1d07065f4a50c1d5be5051e756559a
Reviewed-on: https://review.whamcloud.com/46040
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>