net/virtio: flush Rx queues on start

net/virtio: flush Rx queues on start

After starting a device, the driver shouldn't deliver the
packets that already existed before the device is started
to applications. Otherwise it will lead to incorrect packet
collection for port state. This patch fixes this issue by
flushing the Rx queues when starting the device.

Fixes: a85786dc816f ("virtio: fix states handling during initialization")
Cc: stable@dpdk.org
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>