ns: validation of NS fails on old kernels

[steveej]

The ns package will not work properly on older kernels that don't mount network namespaces with the NSFS. This happens on Semaphore CI today.

This is an example failure message:

failed to create namespace: /proc/18768/task/18798/ns/net is not of type NS

Reproduction of the problem using ip

Semaphore: ~/rkt $ sudo ip netns add newns; mount | grep newns
proc on /run/netns/newns type proc (rw,nosuid,nodev,noexec,relatime)
$ uname -a
Linux semaphore-1605 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux