Rename nsproxy.pid_ns to nsproxy.pid_ns_for_children

nsproxy.pid_ns is *not* the task's pid namespace.  The name should clarify
that.

This makes it more obvious that setns on a pid namespace is weird --
it won't change the pid namespace shown in procfs.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/linux/nsproxy.h
Simple merge

diff --cc kernel/fork.c
Simple merge

diff --cc kernel/nsproxy.c
Simple merge

diff --cc kernel/pid_namespace.c
Simple merge