samples/pktgen: update sample03, no need for clones when bursting

Like sample05, don't use pktgen clone_skb feature when using 'burst' feature,
it is not really needed.  This brings the burst users in sync.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>