[GIT PULL] namespaces related fixes for v4.11-rc1

[Aleksa Sarai]

> The only known user of this prctl systemd
> forks all children after the prctl.  So no userspace regressions will
> occur.

Note that runC and containerd (and thus Docker) as well as cri-o use the 
prctl as well -- to be able to collect exit codes from a non-child 
process (namely to collect the exit code from PID 1 in the container).

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/