ixgbe: dcb, do not tag tc_prio_control frames

The network stack indicate packets should not be DCB
tagged by setting the priority to TC_PRIO_CONTROL. One
usage for this is lldp frames which are not suppossed
to be tagged.
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -6075,7 +6075,8 @@ static netdev_tx_t ixgbe_xmit_frame(struct sk_buff *skb,
 		}
 		tx_flags <<= IXGBE_TX_FLAGS_VLAN_SHIFT;
 		tx_flags |= IXGBE_TX_FLAGS_VLAN;
-	} else if (adapter->flags & IXGBE_FLAG_DCB_ENABLED) {
+	} else if (adapter->flags & IXGBE_FLAG_DCB_ENABLED &&
+		   skb->priority != TC_PRIO_CONTROL) {
 		tx_flags |= ((skb->queue_mapping & 0x7) << 13);
 		tx_flags <<= IXGBE_TX_FLAGS_VLAN_SHIFT;
 		tx_flags |= IXGBE_TX_FLAGS_VLAN;