net: make ethtool_ops const

Auditing all usage of ethtool_ops found several drivers that
are not declaring the struct const when it should be.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
index 7b6b43d..e83d12c 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
@@ -1963,7 +1963,7 @@
 	return -EOPNOTSUPP;
 }
 
-static struct ethtool_ops cxgb_ethtool_ops = {
+static const struct ethtool_ops cxgb_ethtool_ops = {
 	.get_settings      = get_settings,
 	.set_settings      = set_settings,
 	.get_drvinfo       = get_drvinfo,