ipv6: Silence privacy extensions initialization

When a network namespace is created (via CLONE_NEWNET), the loopback
interface is automatically added to the new namespace, triggering a
printk in ipv6_add_dev() if CONFIG_IPV6_PRIVACY is set.

This is problematic for applications which use CLONE_NEWNET as
part of a sandbox, like Chromium's suid sandbox or recent versions of
vsftpd. On a busy machine, it can lead to thousands of useless
"lo: Disabled Privacy Extensions" messages appearing in dmesg.

It's easy enough to check the status of privacy extensions via the
use_tempaddr sysctl, so just removing the printk seems like the most
sensible solution.
Signed-off-by: NRomain Francoise <romain@orebokech.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -420,9 +420,6 @@ static struct inet6_dev * ipv6_add_dev(struct net_device *dev)
 	    dev->type == ARPHRD_TUNNEL6 ||
 	    dev->type == ARPHRD_SIT ||
 	    dev->type == ARPHRD_NONE) {
-		printk(KERN_INFO
-		       "%s: Disabled Privacy Extensions\n",
-		       dev->name);
 		ndev->cnf.use_tempaddr = -1;
 	} else {
 		in6_dev_hold(ndev);