net: constify netif_is_* helpers net_device param

As suggested by Eric, these helpers should have const dev param.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index d1706e8..e5c3954 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5734,7 +5734,7 @@
 
 
 int dev_get_nest_level(struct net_device *dev,
-		       bool (*type_check)(struct net_device *dev))
+		       bool (*type_check)(const struct net_device *dev))
 {
 	struct net_device *lower = NULL;
 	struct list_head *iter;