addrconf: refuse isatap eui64 for INADDR_ANY

A tunnel with no local ipv4 endpoint would otherwise use the
ISATAP linklocal address fe80::5efe:0:0, which is invalid. Rather not
add a linklocal address at all.
Signed-off-by: NSascha Hlusiak <contact@saschahlusiak.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -1520,6 +1520,8 @@ static int addrconf_ifid_infiniband(u8 *eui, struct net_device *dev)
 
 int __ipv6_isatap_ifid(u8 *eui, __be32 addr)
 {
+	if (addr == 0)
+		return -1;
 	eui[0] = (ipv4_is_zeronet(addr) || ipv4_is_private_10(addr) ||
 		  ipv4_is_loopback(addr) || ipv4_is_linklocal_169(addr) ||
 		  ipv4_is_private_172(addr) || ipv4_is_test_192(addr) ||