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/ppp_generic.c b/drivers/net/ppp_generic.c
index 965adb61..0a56a77 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -184,7 +184,7 @@
 static atomic_t channel_count = ATOMIC_INIT(0);
 
 /* per-net private data for this module */
-static int ppp_net_id;
+static int ppp_net_id __read_mostly;
 struct ppp_net {
 	/* units to ppp mapping */
 	struct idr units_idr;