nfp: fix port stats for mac representors

Previously we swapped the tx_packets, tx_bytes and tx_dropped counters
with rx_packets, rx_bytes and rx_dropped counters, respectively. This
behaviour is correct and expected for VF representors but it should not
be swapped for physical port mac representors.

Fixes: eadfa4c3

 ("nfp: add stats and xmit helpers for representors")
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>