pktgen: create num frags requested

Pktgen doesn't generate number of frags requested.
Divide packet size by number of frags and fill that in every frags.

Example:
With packet size 1470, it generate only 11 frags. Initial frags
get lenght 706, 353, 177....so on. Last frag get divided by 2.

Now with this fix, each frags will get 78 bytes.

Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>