pidns: Export free_pid_ns

There is a least one modular user so export free_pid_ns so modules can
capture and use the pid namespace on the very rare occasion when it
makes sense.

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/pid_namespace.c

@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 #include <linux/proc_fs.h>
 #include <linux/reboot.h>
+#include <linux/export.h>
 
 #define BITS_PER_PAGE		(PAGE_SIZE*8)
 
@@ -144,6 +145,7 @@ void free_pid_ns(struct kref *kref)
 	if (parent != NULL)
 		put_pid_ns(parent);
 }
+EXPORT_SYMBOL_GPL(free_pid_ns);
 
 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 {