When restoring on a different node, it may happen that pid_max is
below one of the pid we wanted to recreate.
This leads to a restore error when cloning the restarted process:

(00.011172) Forking task with 44794 pid (flags 0x0)
(00.011205) Error (cr-restore.c:1008): 44794: Write 44793 to sys/kernel/ns_last_pid: Invalid argument

This patch computes the largest pid value and sets the kernel pid_max if
necessary.

If the user don't have the permission to do so, the restart is
failing mentioning that we can't push the pid_max limit.
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>