r6270: Move the VUID handling to a IDR tree. This should avoid O(n)

r6270: Move the VUID handling to a IDR tree.  This should avoid O(n)
behaviour on session setups, and because we no longer need do deal
with the linked list as much, the code is much simpiler too.

We may be able to compleatly remove the tid and vuid linked lists, but
I need to check.

This patch also tries to clean up the VUID handling and session setups
in general.  To avoid security issues, we now have a distinction
between VUIDs allocated for the session setup (to tie togeather the
multiple round trips) and those used after authentication.

Andrew Bartlett
(This used to be commit 3e5775146d9ce6f0ac43aecae7e899b5324399ad)