This partially reverts commit 41210597. Now that b4e4cbeb2 has
been merged Direct IO can be enabled by default for Linux, but
for FreeBSD there still remains a potentially insufficient range
locking in zfs_getpages() which needs to be resolved.
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#16629