Revert "LU-3573 osd-zfs: Only advance zap cursor as needed"

This reverts commit 1da9b84b39ab36be9ba67a72ae175dde6521769b.

This patch introduced a far more serious regression in conf-sanity
test_32b LU-5924 and should be reverted until the problem is fixed.

Change-Id: I28f04a33d1c1bb4688d2ba9af6015a2737fb1d93
Reviewed-on: http://review.whamcloud.com/12887
Tested-by: Jenkins
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>