pktgen: introduce a general func dev_set_key_value()

This is useful for option which is still exerimental.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
pktgen: intro option "-b" for bursting

This is still an experimental option that have not been
accepted into the kernel yet.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
pktgen: introduce param "-c" for setting CLONE_SKB number

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