pktgen: bug fix in transmission headers with frags=0

(bug introduced by commit 26ad787962
(pktgen: speedup fragmented skbs)

The headers of pktgen were incorrectly added in a pktgen packet
without frags (frags=0). There was an offset in the pktgen headers.

The cause was in reusing the pgh variable as a return variable in skb_put
when adding the payload to the skb.

Signed-off-by: Daniel Turull <daniel.turull@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

net/core/pktgen.c

@@ -2620,8 +2620,7 @@ static void pktgen_finalize_skb(struct pktgen_dev *pkt_dev, struct sk_buff *skb,
 	datalen -= sizeof(*pgh);
 
 	if (pkt_dev->nfrags <= 0) {
-		pgh = (struct pktgen_hdr *)skb_put(skb, datalen);
-		memset(pgh + 1, 0, datalen);
+		memset(skb_put(skb, datalen), 0, datalen);
 	} else {
 		int frags = pkt_dev->nfrags;
 		int i, len;