hv_netvsc: fix bogus ifalias on network device

If the guest network adapter is not configured with DeviceNaming
enabled on the host, then the query for friendly name will return
success but with a zero length name. Which then leads to a garbage value
(stack contents) for ifalias.

Fix is simple, just don't set name if  host doesn't return it.

Fixes: 0fe554a4 ("hv_netvsc: propogate Hyper-V friendly name into interface alias")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/rndis_filter.c

@@ -1237,7 +1237,10 @@ static void rndis_get_friendly_name(struct net_device *net,
 	if (rndis_filter_query_device(rndis_device, net_device,
 				      RNDIS_OID_GEN_FRIENDLY_NAME,
 				      wname, &size) != 0)
-		return;
+		return;	/* ignore if host does not support */
+
+	if (size == 0)
+		return;	/* name not set */
 
 	/* Convert Windows Unicode string to UTF-8 */
 	len = ucs2_as_utf8(ifalias, wname, sizeof(ifalias));