net: Export open_related_ns()

This function will be used to obtain net of tun device.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

fs/nsfs.c

@@ -184,6 +184,7 @@ int open_related_ns(struct ns_common *ns,
 
 	return fd;
 }
+EXPORT_SYMBOL_GPL(open_related_ns);
 
 static long ns_ioctl(struct file *filp, unsigned int ioctl,
 			unsigned long arg)