seccomp: add arch_prctl() to the syscall whitelist

seccomp: add arch_prctl() to the syscall whitelist

It appears that even a very simple /etc/qemu-ifup configuration can
require the arch_prctl() syscall, see the example below:

	#!/bin/sh
	/sbin/ifconfig $1 0.0.0.0 up
	/usr/sbin/brctl addif <switch> $1

Signed-off-by: Paul Moore <pmoore@redhat.com>
Reviewed-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
Message-id: 20130718135703.8247.19213.stgit@localhost
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit d2509b667caf482b6f827ff2645cbeb9b39ce29e)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>