SELinux: renumber the superblock options

Just to make it clear that we have mount time options and flags,
separate them.  Since I decided to move the non-mount options above
above 0x10, we need a short instead of a char.  (x86 padding says
this takes up no additional space as we have a 3byte whole in the
structure)

Signed-off-by: Eric Paris <eparis@redhat.com>