net/ipv6: don't reinitialize ndev->cnf.addr_gen_mode on new inet6_dev

The value has already been copied from this netns's devconf_dflt, it
shouldn't be reset to the global kernel default.

Fixes: d35a00b8 ("net/ipv6: allow sysctl to change link-local address generation mode")
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Reviewed-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -385,8 +385,6 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
 
 	if (ndev->cnf.stable_secret.initialized)
 		ndev->cnf.addr_gen_mode = IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
-	else
-		ndev->cnf.addr_gen_mode = ipv6_devconf_dflt.addr_gen_mode;
 
 	ndev->cnf.mtu6 = dev->mtu;
 	ndev->nd_parms = neigh_parms_alloc(dev, &nd_tbl);