dcb: Add DCBX capabilities bitmask to the get_ieee response

Adding the capabilities bitmask to the get_ieee response allows
user space to determine the current DCBX mode. Either CEE or IEEE
this is useful with devices that support switching between modes
where knowing the current state is relevant.

Derived from work by Mark Rustad
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dcb/dcbnl.c

@@ -1288,6 +1288,7 @@ static int dcbnl_ieee_get(struct net_device *netdev, struct nlattr **tb,
 	struct nlattr *ieee, *app;
 	struct dcb_app_type *itr;
 	const struct dcbnl_rtnl_ops *ops = netdev->dcbnl_ops;
+	int dcbx;
 	int err;
 
 	if (!ops)
@@ -1338,6 +1339,12 @@ static int dcbnl_ieee_get(struct net_device *netdev, struct nlattr **tb,
 			}
 		}
 	}
+
+	if (netdev->dcbnl_ops->getdcbx)
+		dcbx = netdev->dcbnl_ops->getdcbx(netdev);
+	else
+		dcbx = -EOPNOTSUPP;
+
 	spin_unlock(&dcb_lock);
 	nla_nest_end(skb, app);
 
@@ -1366,6 +1373,11 @@ static int dcbnl_ieee_get(struct net_device *netdev, struct nlattr **tb,
 	}
 
 	nla_nest_end(skb, ieee);
+	if (dcbx >= 0) {
+		err = nla_put_u8(skb, DCB_ATTR_DCBX, dcbx);
+		if (err)
+			goto nla_put_failure;
+	}
 	nlmsg_end(skb, nlh);
 
 	return rtnl_unicast(skb, &init_net, pid);