tun: add missing rx stats accounting in tun_xdp_act

The TUN can be used as vhost-net backend, and it is necessary to
count the packets transmitted from TUN to vhost-net/virtio-net.
However, there are some places in the receive path that were not
taken into account when using XDP. It would be beneficial to also
include new accounting for successfully received bytes using
dev_sw_netstats_rx_add.

Fixes: 761876c8 ("tap: XDP support")
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>