LU-18886 zfs-osd: za_name flexible array OI scrub fix

LU-18886 zfs-osd: za_name flexible array OI scrub fix

Initialize the zap_attribute_t.za_name_len to resolve the
OI scrub failures observed with zfs-2.3.  This is a follow up
to commit d47a71f7a894a193957fe7771d43c5767979c117 which made
an identical fix for the other sites where a zap_attribute_t
is used.

Test-Parameters: fstype=zfs
Fixes: d47a71f7a894a ("LU-18360 zfs-osd: za_name flexible array")
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Change-Id: Ib4295cbb7ce7e7efe0f7e67b82bc8c73a1f9df8d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58762
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>