When PFC is enabled for any UP in single TC configuration the driver didn't
collect the PFC XOFF RX stats. Though a single TC with PFC enabled is not a
common scenario do not prevent the driver from collecting stats if firmware
indicates that PFC is enabled.

Change-ID: Ie20bd58b07608b528f3c6d95894c9ae56b00077a
Signed-off-by: NNeerav Parikh <neerav.parikh@intel.com>
Tested-by: NJim Young <james.m.young@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>