5841 NFSv3 writes underneath mounted filesystem to directory

Review Request #31 — Created April 14, 2015 and updated — Latest diff uploaded


webrev: http://cr.illumos.org/~webrev/marcel/il-zfs-mnt-protect/

This adds a protection of empty ZFS mount points to NFSv2/3 server implementation.

I tested all NFS operations from both NFSv2 and NFSv3 clients to make sure the
fix works as expected. I confirmed that the NFS server protects empty ZFS
mount points only (with the access denied error). Non-empty ZFS mount points
and mount points for other filesystems are not protected. I also tested basic
NFSv4 functionality to make sure there is no regression introduced.