Implement .vop_pathconf and .vop_getacl for the .zfs ctldir
zfsctl_pathconf will report all the same variables that regular ZFS volumes
report. zfs_common_getacl will report an ACL equivalent to 555, except that
you can't read xattrs or edit attributes.
Fixes a bug where "ls .zfs" will occasionally print something like:
ls: .zfs/.: Operation not supported