libxc: limit cpu values when setting vcpu affinity

libxc: limit cpu values when setting vcpu affinity

When support for pinning more than 64 cpus was added, check for cpu
out-of-range values was removed. This can lead to subsequent
out-of-bounds cpumap array accesses in case the cpu number is higher
than the actual count.

This patch returns the check.

This is CVE-2013-2072 / XSA-56

Signed-off-by: Petr Matousek <pmatouse@redhat.com>
master commit: 41abbadef60e5fccdfd688579dd458f7f7887cf5
master date: 2013-05-29 15:49:22 +0100