pktgen: Remove redundant clone_skb override

When the netif_receive xmit_mode is set, a line is supposed to set
clone_skb to a default 0 value. This line is made redundant due to a
preceding line that checks if clone_skb is more than zero and returns
-ENOTSUPP.

Overriding clone_skb to 0 does not make any difference to the behavior
because if it was positive we return error. So it can be either 0 or
negative, and in both cases the behavior is the same.

Remove redundant line that sets clone_skb to zero.

Signed-off-by: Nick Richardson <richardsonnick@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>