pktgen: fix packet generation

pkt_gen->last_ok was not set properly, so after the first burst
pktgen instead of allocating new packet, will reuse old one, advance
eth_type_trans further, which would mean the stack will be seeing very
short bogus packets.

Fixes: 62f64aed622b ("pktgen: introduce xmit_mode '<start_xmit|netif_receive>'")
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -1189,6 +1189,16 @@ static ssize_t pktgen_if_write(struct file *file,
 				return -ENOTSUPP;
 
 			pkt_dev->xmit_mode = M_NETIF_RECEIVE;
+
+			/* make sure new packet is allocated every time
+			 * pktgen_xmit() is called
+			 */
+			pkt_dev->last_ok = 1;
+
+			/* override clone_skb if user passed default value
+			 * at module loading time
+			 */
+			pkt_dev->clone_skb = 0;
 		} else {
 			sprintf(pg_result,
 				"xmit_mode -:%s:- unknown\nAvailable modes: %s",
@@ -3415,7 +3425,6 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
 				/* get out of the loop and wait
 				 * until skb is consumed
 				 */
-				pkt_dev->last_ok = 1;
 				break;
 			}
 			/* skb was 'freed' by stack, so clean few