pktgen: Allow on loopback device

When pktgen is used to measure the performance of dev_queue_xmit()
packet handling in the core, it is preferable to not hand down
packets to a low-level Ethernet driver as it would distort the
measurements.

Allow using pktgen on the loopback device, thus constraining
measurements to core code.
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -2003,8 +2003,8 @@ static int pktgen_setup_dev(const struct pktgen_net *pn,
 		return -ENODEV;
 	}
 
-	if (odev->type != ARPHRD_ETHER) {
-		pr_err("not an ethernet device: \"%s\"\n", ifname);
+	if (odev->type != ARPHRD_ETHER && odev->type != ARPHRD_LOOPBACK) {
+		pr_err("not an ethernet or loopback device: \"%s\"\n", ifname);
 		err = -EINVAL;
 	} else if (!netif_running(odev)) {
 		pr_err("device is down: \"%s\"\n", ifname);