The loop to read packets does not take all packets as the number of
available packets (nb_used) is decremented in the loop.
Fixes: 52b5a707e6 ("net/virtio: add Altivec Rx")
Signed-off-by: David Christensen <drc@linux.vnet.ibm.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>