Previously, J_KEY generation was based on the lower 16 bits
of the user's UID. While this works, it was not good enough
as a non-root user could collide with a root user given a
sufficiently large UID.

This patch attempt to improve the J_KEY generation by using
the following algorithm:

The 16 bit J_KEY space is partitioned into 3 separate spaces
reserved for different user classes:
   * all users with administtor privileges (including 'root')
     will use J_KEYs in the range of 0 to 31,
   * all kernel protocols, which use KDETH packets will use
     J_KEYs in the range of 32 to 63, and
   * all other users will use J_KEYs in the range of 64 to
     65535.

The above separation is aimed at preventing different user levels
from sending packets to each other and, additionally, separate
kernel protocols from all other types of users. The later is meant
to prevent the potential corruption of kernel memory by any other
type of user.
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>