ixgbe: move tc variable to CONFIG_IXGBE_DCB

tc is required by CONFIG_IXGBE_DCB.
This also fixes compilation warning:

 drivers/net/ixgbe/ixgbe_main.c: In function ‘ixgbe_tx_is_paused’:
 drivers/net/ixgbe/ixgbe_main.c:245: warning: unused variable ‘tc’

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -240,11 +240,11 @@ static void ixgbe_unmap_and_free_tx_resource(struct ixgbe_adapter *adapter,
 static inline bool ixgbe_tx_is_paused(struct ixgbe_adapter *adapter,
                                       struct ixgbe_ring *tx_ring)
 {
-	int tc;
 	u32 txoff = IXGBE_TFCS_TXOFF;
 
 #ifdef CONFIG_IXGBE_DCB
 	if (adapter->flags & IXGBE_FLAG_DCB_ENABLED) {
+		int tc;
 		int reg_idx = tx_ring->reg_idx;
 		int dcb_i = adapter->ring_feature[RING_F_DCB].indices;