estates: reuse same estate for extra_undefined()

estates: reuse same estate for extra_undefined()

Using the same state here save a little memory.  It lets us merge two
undefined states and get the same state as a result so that simplifies
the debugging output a bit and makes the ->possible list shorter.

The problem is when the estate_undefined, has a related list then we need
to make a copy of that.  So I had to introduce set_related() to handle
that.

It's not a perfect situation.  Really I would prefer to reuse estates as
much as possible.  So this is only a step in that direction.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>