Same idea as commit a287ac28919d ("vhost: allocate and free packets
in bulk in Tx packed"), allocate and free packets in bulk.
Also remove the unused function virtio_dev_pktmbuf_alloc.
Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>