Update zfs-functions.in

[allen-4]

Motivation and Context

Closes #10341
Related to bug #10341 and #10376
The init.d zfs-share script does not perform the intended action without having a variable set for ZFS_SHARE and ZFS_UNSHARE

Description

Assign default values to ZFS_SHARE and ZFS_UNSHARE. Export the environment variables after sourcing the configuration file.

How Has This Been Tested?

Tested on gentoo with kernel version 5.6.14

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• [ x] My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• [x ] I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[codecov-commenter]

Codecov Report

Merging #10382 into master will decrease coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10382      +/-   ##
==========================================
- Coverage   79.36%   79.22%   -0.15%     
==========================================
  Files         391      391              
  Lines      123585   123585              
==========================================
- Hits        98086    97907     -179     
- Misses      25499    25678     +179     

Flag	Coverage Δ
#kernel	79.97% <ø> (+0.01%)	⬆️
#user	64.28% <ø> (-0.99%)	⬇️

Impacted Files	Coverage Δ
module/icp/algs/modes/gcm.c	77.04% <0.00%> (-4.77%)	⬇️
module/lua/lmem.c	83.33% <0.00%> (-4.17%)	⬇️
module/zfs/vdev_raidz.c	89.65% <0.00%> (-2.95%)	⬇️
module/zfs/vdev_removal.c	93.90% <0.00%> (-2.76%)	⬇️
module/zfs/vdev_indirect_mapping.c	96.61% <0.00%> (-1.94%)	⬇️
module/zfs/metaslab.c	94.12% <0.00%> (-1.67%)	⬇️
module/zfs/zio.c	87.12% <0.00%> (-1.54%)	⬇️
module/zfs/vdev_queue.c	94.62% <0.00%> (-1.50%)	⬇️
module/zfs/vdev_indirect.c	73.33% <0.00%> (-1.34%)	⬇️
cmd/ztest/ztest.c	74.11% <0.00%> (-1.29%)	⬇️
... and 42 more

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[behlendorf]

@gyakovlev @ryao would you mind reviewing this.

[behlendorf]

@allen-4 thanks for looking in to this. Could you please your signed-off-by to the commit message and update the PR.

[ryao]

LGTM

[allen-4]

@behlendorf Thank you, I added my sign-off. Hope I got it right, I'm very new to github.

[gyakovlev]

LGTM
as I said before re-ordering and exporting those variables is not technically required but logically correct, and good thing to do.
it will make sure external processes receive consistent environment.
script scope env already used overrides from conf.d file.