cgroups: remove deprecated subsystem from examples.

The 'ns' cgroup is considered deprecated. Change the cgroup subsystem
used in the examples of the cgroup documentation from 'ns' to 'blkio'.
Signed-off-by: NTrevor Woerner <twoerner@gmail.com>
Acked-by: NLi Zefan <lizf@cn.fujitsu.com>
Acked-by: NPaul Menage <menage@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/cgroups/cgroups.txt

@@ -355,13 +355,13 @@ subsystems, type:
 
 To change the set of subsystems bound to a mounted hierarchy, just
 remount with different options:
-# mount -o remount,cpuset,ns hier1 /dev/cgroup
+# mount -o remount,cpuset,blkio hier1 /dev/cgroup
 
-Now memory is removed from the hierarchy and ns is added.
+Now memory is removed from the hierarchy and blkio is added.
 
-Note this will add ns to the hierarchy but won't remove memory or
+Note this will add blkio to the hierarchy but won't remove memory or
 cpuset, because the new options are appended to the old ones:
-# mount -o remount,ns /dev/cgroup
+# mount -o remount,blkio /dev/cgroup
 
 To Specify a hierarchy's release_agent:
 # mount -t cgroup -o cpuset,release_agent="/sbin/cpuset_release_agent" \