ethtool: Don't omit the netlink reply if no features were changed

The legacy ethtool userspace tool shows an error when no features could
be changed. It's useful to have a netlink reply to be able to show this
error when __netdev_update_features wasn't called, for example:

1. ethtool -k eth0
   large-receive-offload: off
2. ethtool -K eth0 rx-fcs on
3. ethtool -K eth0 lro on
   Could not change any device features
   rx-lro: off [requested on]
4. ethtool -K eth0 lro on
   # The output should be the same, but without this patch the kernel
   # doesn't send the reply, and ethtool is unable to detect the error.

This commit makes ethtool-netlink always return a reply when requested,
and it still avoids unnecessary calls to __netdev_update_features if the
wanted features haven't changed.

Fixes: 0980bfcd ("ethtool: set netdev features with FEATURES_SET request")
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/features.c

@@ -268,14 +268,11 @@ int ethnl_set_features(struct sk_buff *skb, struct genl_info *info)
 	bitmap_and(req_wanted, req_wanted, req_mask, NETDEV_FEATURE_COUNT);
 	bitmap_andnot(new_wanted, old_wanted, req_mask, NETDEV_FEATURE_COUNT);
 	bitmap_or(req_wanted, new_wanted, req_wanted, NETDEV_FEATURE_COUNT);
-	if (bitmap_equal(req_wanted, old_wanted, NETDEV_FEATURE_COUNT)) {
-		ret = 0;
-		goto out_rtnl;
-	}
-
+	if (!bitmap_equal(req_wanted, old_wanted, NETDEV_FEATURE_COUNT)) {
 		dev->wanted_features &= ~dev->hw_features;
 		dev->wanted_features |= ethnl_bitmap_to_features(req_wanted) & dev->hw_features;
 		__netdev_update_features(dev);
+	}
 	ethnl_features_to_bitmap(new_active, dev->features);
 	mod = !bitmap_equal(old_active, new_active, NETDEV_FEATURE_COUNT);