drivers/net: const-ify ethtool_ops declarations

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/cassini.c b/drivers/net/cassini.c
index 7ed3764..275057c 100644
--- a/drivers/net/cassini.c
+++ b/drivers/net/cassini.c
@@ -4812,7 +4812,7 @@
 	BUG_ON(i != CAS_NUM_STAT_KEYS);
 }
 
-static struct ethtool_ops cas_ethtool_ops = {
+static const struct ethtool_ops cas_ethtool_ops = {
 	.get_drvinfo		= cas_get_drvinfo,
 	.get_settings		= cas_get_settings,
 	.set_settings		= cas_set_settings,