kernel: make taskstats available from all net namespaces

If getdelays runs in a non-init network namespace, it will fail in getting
delayacct stats even if it has privilege of root user, which seems to be
not very reasonable. We can simply reproduce this by executing commands:

unshare -n
getdelays -d -p <pid>

I don't think net namespace should be an obstacle to the normal execution
of getdelay function. So let's make it available from all net namespaces.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: xu xin <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Cc: Yang Yang <[e-mail]>
Cc: "Dr. Thomas Orgis" <[e-mail]>
Cc: Eric W. Biederman <[e-mail]>
Cc: Ismael Luceno <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

kernel/taskstats.c

···
 	.module		= THIS_MODULE,
 	.ops		= taskstats_ops,
 	.n_ops		= ARRAY_SIZE(taskstats_ops),
+	.netnsok	= true,
 };
 
 /* Needed early in initialization */