[NET]: Zero out SIOCGIFHWADDR buffer if dev->addr_len is zero.

This preserves 2.4.x behavior.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2376,6 +2376,9 @@ static int dev_ifsioc(struct ifreq *ifr, unsigned int cmd)
 			return dev_set_mtu(dev, ifr->ifr_mtu);
 
 		case SIOCGIFHWADDR:
+			if (!dev->addr_len)
+				memset(ifr->ifr_hwaddr.sa_data, 0, sizeof ifr->ifr_hwaddr.sa_data);
+			else
 				memcpy(ifr->ifr_hwaddr.sa_data, dev->dev_addr,
 				       min(sizeof ifr->ifr_hwaddr.sa_data, (size_t) dev->addr_len));
 			ifr->ifr_hwaddr.sa_family = dev->type;