Cross-platform acltype

The acltype property is currently hidden on FreeBSD and does not
reflect the NFSv4 style ZFS ACLs used on the platform.  This makes it
difficult to observe that a pool imported from FreeBSD on Linux has a
different type of ACL that is being ignored, and vice versa.

Add an nfsv4 acltype and expose the property on FreeBSD.

Make the default acltype nfsv4 on FreeBSD.

Setting acltype to an unhanded style is treated the same as setting
it to off.  The ACLs will not be removed, but they will be ignored.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10520

module/os/linux/zfs/zfs_acl.c

@@ -2666,7 +2666,7 @@ zfs_zaccess(znode_t *zp, int mode, int flags, boolean_t skipaclchk, cred_t *cr)
 
 /*
  * Translate traditional unix S_IRUSR/S_IWUSR/S_IXUSR mode into
- * native ACL format and call zfs_zaccess()
+ * NFSv4-style ZFS ACL format and call zfs_zaccess()
  */
 int
 zfs_zaccess_rwx(znode_t *zp, mode_t mode, int flags, cred_t *cr)

module/os/linux/zfs/zfs_vfsops.c

@@ -352,6 +352,7 @@ acltype_changed_cb(void *arg, uint64_t newval)
 	zfsvfs_t *zfsvfs = arg;
 
 	switch (newval) {
+	case ZFS_ACLTYPE_NFSV4:
 	case ZFS_ACLTYPE_OFF:
 		zfsvfs->z_acl_type = ZFS_ACLTYPE_OFF;
 		zfsvfs->z_sb->s_flags &= ~SB_POSIXACL;