ixgbe: only check pfc bits in hang logic if pfc is enabled

Only check pfc bits in hang logic if PFC is enabled.  Previously,
if DCB was enabled but PFC was disabled the incorrect pause
bits would be checked.
Signed-off-by: NJohn Fastabend <john.r.fastabend@intel.com>
Acked-by: NDon Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -642,7 +642,7 @@ static inline bool ixgbe_tx_xon_state(struct ixgbe_adapter *adapter,
 	u32 txoff = IXGBE_TFCS_TXOFF;
 
 #ifdef CONFIG_IXGBE_DCB
-	if (adapter->flags & IXGBE_FLAG_DCB_ENABLED) {
+	if (adapter->dcb_cfg.pfc_mode_enable) {
 		int tc;
 		int reg_idx = tx_ring->reg_idx;
 		int dcb_i = adapter->ring_feature[RING_F_DCB].indices;