ns proc: Enable setns for support for the pid namespace

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 2e0331e..79bf459 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -246,12 +246,9 @@
 
 static int pidns_install(struct nsproxy *nsproxy, void *ns)
 {
-	return -EINVAL;
-#ifdef notyet
 	put_pid_ns(nsproxy->pid_ns);
 	nsproxy->pid_ns = get_pid_ns(ns);
 	return 0;
-#endif
 }
 
 static unsigned int pidns_inum(void *vns)