net: enetc: correct rx_bytes statistics of XDP

The rx_bytes statistics of XDP are always zero, because rx_byte_cnt
is not updated after it is initialized to 0. So fix it.

Fixes: d1b15102 ("net: enetc: add support for XDP_DROP and XDP_PASS")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>