virtio_net: ensure netdev_tx_reset_queue is called on bind xsk for tx

virtnet_sq_bind_xsk_pool() flushes tx skbs and then resets tx queue, so
DQL counters need to be reset when flushing has actually occurred, Add
virtnet_sq_free_unused_buf_done() as a callback for virtqueue_resize()
to handle this.

Fixes: 21a4e3ce ("virtio_net: xsk: bind/unbind xsk for tx")
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>