ovl: fix wrong detection of 32bit inode numbers

ovl: fix wrong detection of 32bit inode numbers

The implicit FILEID_INO32_GEN encoder was changed to be explicit,
so we need to fix the detection.

When mounting overlayfs with upperdir and lowerdir on different ext4
filesystems, the expected kmsg log is:

  overlayfs: "xino" feature enabled using 32 upper inode bits.

But instead, since the regressing commit, the kmsg log was:

  overlayfs: "xino" feature enabled using 2 upper inode bits.

Fixes: e21fc2038c1b9 ("exportfs: make ->encode_fh() a mandatory method for NFS export")
Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>