FreeBSD: Add zfs_link_create() error handling

Originally Solaris didn't expect errors there, but they may happen
if we fail to add entry into ZAP. Linux fixed it in #7421, but it
was never fully ported to FreeBSD.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #13215
Closes #16138