nfp: validate the return code from dev_queue_xmit()

dev_queue_xmit() may return error codes as well as netdev_tx_t,
and it always consumes the skb.  Make sure we always return a
correct netdev_tx_t value.

Fixes: eadfa4c3 ("nfp: add stats and xmit helpers for representors")
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NJohn Hurley <john.hurley@netronome.com>
Reviewed-by: NSimon Horman <simon.horman@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfp_net_repr.c

@@ -195,7 +195,7 @@ static netdev_tx_t nfp_repr_xmit(struct sk_buff *skb, struct net_device *netdev)
 	ret = dev_queue_xmit(skb);
 	nfp_repr_inc_tx_stats(netdev, len, ret);
 
-	return ret;
+	return NETDEV_TX_OK;
 }
 
 static int nfp_repr_stop(struct net_device *netdev)