LU-8619 osd: define DN_MAX_BONUSLEN

LU-8619 osd: define DN_MAX_BONUSLEN

ZFS master doesn't define DN_MAX_BONUSLEN which is still used
by osd-zfs - define it as DN_OLD_MAX_BONUSLEN.

Change-Id: Ieec310ee4d368cae7c5c93808caddb0db0b08fc7
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/22523
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>