i40e: Fix reset bw limit when DCB enabled with 1 TC

There was an AQ error I40E_AQ_RC_EINVAL when trying
to reset bw limit as part of bw allocation setup.
This was caused by trying to reset bw limit with
DCB enabled. Bw limit should not be reset when
DCB is enabled. The code was relying on the pf->flags
to check if DCB is enabled but if only 1 TC is available
this flag will not be set even though DCB is enabled.
Add a check for number of TC and if it is 1
don't try to reset bw limit even if pf->flags shows
DCB as disabled.

Fixes: fa38e30 ("i40e: Fix for Tx timeouts when interface is brought up if DCB is enabled")
Suggested-by: Alexander Lobakin <alexandr.lobakin@intel.com> # Flatten the condition
Signed-off-by: Sylwester Dziedziuch <sylwesterx.dziedziuch@intel.com>
Signed-off-by: Jedrzej Jagielski <jedrzej.jagielski@intel.com>
Reviewed-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Tested-by: Imam Hassan Reza Biswas <imam.hassan.reza.biswas@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -5372,14 +5372,24 @@ static int i40e_vsi_configure_bw_alloc(struct i40e_vsi *vsi, u8 enabled_tc,
 	/* There is no need to reset BW when mqprio mode is on.  */
 	if (pf->flags & I40E_FLAG_TC_MQPRIO)
 		return 0;
-	if (!vsi->mqprio_qopt.qopt.hw && !(pf->flags & I40E_FLAG_DCB_ENABLED)) {
+
+	if (!vsi->mqprio_qopt.qopt.hw) {
+		if (pf->flags & I40E_FLAG_DCB_ENABLED)
+			goto skip_reset;
+
+		if (IS_ENABLED(CONFIG_I40E_DCB) &&
+		    i40e_dcb_hw_get_num_tc(&pf->hw) == 1)
+			goto skip_reset;
+
 		ret = i40e_set_bw_limit(vsi, vsi->seid, 0);
 		if (ret)
 			dev_info(&pf->pdev->dev,
 				 "Failed to reset tx rate for vsi->seid %u\n",
 				 vsi->seid);
 		return ret;
 	}
+
+skip_reset:
 	memset(&bw_data, 0, sizeof(bw_data));
 	bw_data.tc_valid_bits = enabled_tc;
 	for (i = 0; i < I40E_MAX_TRAFFIC_CLASS; i++)