nfp: abm: switch to extended stats for reading packet/byte counts

In PRIO-enabled FW read the statistics from per-band symbol, rather
than from the standard per-PCIe-queue counters.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>