pktgen: script for using pktgen new "burst" option

Update script pktgen02_burst.sh, as pktgen option name changed, when
the burst feature were finally accepted in upstream kernels.

The burst option (-b) avoids writing the HW tailptr on every driver xmit.
The performance boost is impressive, see commit link.
If correctly tuned, single CPU 10G wirespeed small pkts 14.8Mpps is possible.

Needed tuning see:
 http://netoptimizer.blogspot.dk/2014/06/pktgen-for-network-overload-testing.html

Avail in kernels since:
  commit 38b2cf2982dc73 ("net: pktgen: packet bursting via skb->xmit_more")
  https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=38b2cf2982dc73

 burst=1 is the default. It sends one packet with xmit_more=false
 burst=2 sends one packet with xmit_more=true and
         2nd copy of the same packet with xmit_more=false
 burst=3 sends two copies of the same packet with xmit_more=true and
         3rd copy with xmit_more=false

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>