Fix incremental receive silently failing for recursive sends

[pcd1193182]

Motivation and Context

See #12661

Description

The problem occurs because dmu_recv_begin pulls in the payload and next header from the input stream in order to use the contents of the begin record's nvlist. However, the change to do that before the other checks in dmu_recv_begin occur caused a regression where an empty send stream in a recursive send could have its END record consumed by this, which broke the logic of recv_skip. A test is also included to protect against this case in the future.

How Has This Been Tested?

Using the reproducer script from the issue.

Types of changes

• 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)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• 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.

[pcd1193182]

In the latest commit I had to remove the "heal" option from the libzfs test, because the heal parameter only works with an existing dataset (and not having it requires not having an existing dataset), which the libzfs input test infrastructure isn't set up for.

[behlendorf]

There's always something, reported by the CI with this change.

http://build.zfsonlinux.org/builders/CentOS%208%20x86_64%20%28TEST%29/builds/11694/steps/shell_4/logs/summary

Test: /usr/share/zfs/zfs-tests/tests/functional/rsend/send-c_verify_contents (run as root) [00:02] [FAIL]
04:33:11.79 ASSERTION: zfs send -c -R send replication stream up to the named snap.
04:33:12.14 SUCCESS: eval zfs send -c -R testpool@final > /mnt/backdir-rsend/pool-final-R
04:33:13.75 SUCCESS: eval zfs receive -d -F testpool2 < /mnt/backdir-rsend/pool-final-R
04:33:13.81 11,15d10
04:33:13.81 < PREFIX/sendfs
04:33:13.81 < PREFIX/sendfs@A
04:33:13.81 < PREFIX/sendfs@B
04:33:13.81 < PREFIX/sendfs@D
04:33:13.81 < PREFIX/sendfs@E
04:33:13.81 ERROR: cmp_ds_subs testpool testpool2 exited 1
04:33:13.81 NOTE: Performing test-fail callback (/usr/share/zfs/zfs-tests/callbacks/zfs_dbgmsg.ksh)