net: mvneta: get rid of xdp_ret in mvneta_swbm_rx_frame

Get rid of xdp_ret in mvneta_swbm_rx_frame routine since now
we can rely on xdp_stats to flush in case of xdp_redirect

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>