LU-8882 osd: use bydnode methods to access DMU

LU-8882 osd: use bydnode methods to access DMU

newer ZFS allows to access DMU by dnode which save expensive
dnode# to dnode_t mapping.

Change-Id: I469c2a72d18f170ebb96dd33c23bb6d8f037188a
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: https://review.whamcloud.com/24035
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>