Include fc00::/8 in the set of local addresses.

The current local address range is fd00::/8, but RFC 4193
para 3.1/3.2 reserves fc00::/8 for future use as local addresses,
so add that to the list.

Thanks to Michalis Vasileiadis for spotting this omission.

src/rfc1035.c

@@ -448,7 +448,7 @@ int private_net6(struct in6_addr *a, int ban_localhost)
     (IN6_IS_ADDR_LOOPBACK(a) && ban_localhost) ||    /* RFC 6303 4.3 */
     IN6_IS_ADDR_LINKLOCAL(a) ||   /* RFC 6303 4.5 */
     IN6_IS_ADDR_SITELOCAL(a) ||
-    ((unsigned char *)a)[0] == 0xfd ||   /* RFC 6303 4.4 */
+    (((unsigned char *)a)[0] & 0xfe) == 0xfc || /* RFC 4196 3.1 */
     ((u32 *)a)[0] == htonl(0x20010db8); /* RFC 6303 4.6 */
 }