jfs: use generic posix ACL infrastructure

Copy the scheme I introduced to btrfs many years ago to only use the
xattr handler for ACLs, but pass plain attrs straight through.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>