LU-8856 osd: mark specific transactions netfree

LU-8856 osd: mark specific transactions netfree

osd-zfs should mark some transactions netfree. this means those transactions
are expected to release space (rather than consume) and for this kind of
transaction half of reserved space is available.

Change-Id: I71605bc224882aafac26b3dfb0f3d7e82af8fde8
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: https://review.whamcloud.com/26930
Tested-by: Jenkins
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>