LU-17630 osc: add cond_resched() to osc_lru_shrink()

LU-17630 osc: add cond_resched() to osc_lru_shrink()

osc_lru_shrink() may need to handle lots of pages and this way
can block scheduling for long. add couple cond_resched() to
prevent kernel warnings and other thread's starvation.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I862c568ac777c0b929a1ffb61e246b079aee6718
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54346
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <patrick.farrell@oracle.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>