igc: Add condition for qbv_config_change_errors counter

Add condition to increase the qbv counter during taprio qbv
configuration only.

There might be a case when TC already been setup then user configure
the ETF/CBS qdisc and this counter will increase if no condition above.

Fixes: ae4fe469

 ("igc: Add qbv_config_change_errors counter")
Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>