Phonet: phonet_net_id can be static (sparse)

Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
index bf5cf69..da564ef 100644
--- a/net/phonet/pn_dev.c
+++ b/net/phonet/pn_dev.c
@@ -44,7 +44,7 @@
 	struct phonet_routes routes;
 };
 
-int phonet_net_id __read_mostly;
+static int phonet_net_id __read_mostly;
 
 static struct phonet_net *phonet_pernet(struct net *net)
 {