ipv6: add flowlabel_consistency sysctl

With the introduction of IPV6_FL_F_REFLECT, there is no guarantee of
flow label unicity. This patch introduces a new sysctl to protect the old
behaviour, enable by default.

Changelog of V3:
 * rename ip6_flowlabel_consistency to flowlabel_consistency
 * use net_info_ratelimited()
 * checkpatch cleanups

Signed-off-by: Florent Fourcot <florent.fourcot@enst-bretagne.fr>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index b51b268..7f405a1 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -31,6 +31,13 @@
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "flowlabel_consistency",
+		.data		= &init_net.ipv6.sysctl.flowlabel_consistency,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec
+	},
 	{ }
 };
 
@@ -59,6 +66,7 @@
 		goto out;
 	ipv6_table[0].data = &net->ipv6.sysctl.bindv6only;
 	ipv6_table[1].data = &net->ipv6.sysctl.anycast_src_echo_reply;
+	ipv6_table[2].data = &net->ipv6.sysctl.flowlabel_consistency;
 
 	ipv6_route_table = ipv6_route_sysctl_init(net);
 	if (!ipv6_route_table)