LU-11408 osc: propagate grant shrink interval immediately

LU-11408 osc: propagate grant shrink interval immediately

currently the new interval (updated with lctl) will be used
only when the next shrink happens. with default interval it
will take at least 20 minutes. instead we should refresh it
immediately.

Change-Id: Id22824e48fbc50c1f464316ab5b574d1189bb0c5
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/33204
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>