netns: net_identifiers should be read_mostly

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index b6e145a..d9deaa7 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -66,7 +66,7 @@
 static void ipip6_tunnel_init(struct net_device *dev);
 static void ipip6_tunnel_setup(struct net_device *dev);
 
-static int sit_net_id;
+static int sit_net_id __read_mostly;
 struct sit_net {
 	struct ip_tunnel *tunnels_r_l[HASH_SIZE];
 	struct ip_tunnel *tunnels_r[HASH_SIZE];