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/drivers/net/pppoe.c b/drivers/net/pppoe.c
index 60c8d23..a1dcba2 100644
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -97,7 +97,7 @@
 static struct ppp_channel_ops pppoe_chan_ops;
 
 /* per-net private data for this module */
-static int pppoe_net_id;
+static int pppoe_net_id __read_mostly;
 struct pppoe_net {
 	/*
 	 * we could use _single_ hash table for all