Fix DHCPv6 address allocation for some pathalogical cases.

src/dnsmasq.h

@@ -992,6 +992,7 @@ struct dhcp_lease *lease4_allocate(struct in_addr addr);
 struct dhcp_lease *lease6_allocate(struct in6_addr *addrp, int lease_type);
 struct dhcp_lease *lease6_find(unsigned char *clid, int clid_len, 
 			       int lease_type, int iaid, struct in6_addr *addr);
+void lease6_filter(int lease_type, int iaid, struct dhcp_context *context);
 struct dhcp_lease *lease6_find_by_addr(struct in6_addr *net, int prefix, u64 addr);
 u64 lease_find_max_addr6(struct dhcp_context *context);
 void lease_ping_reply(struct in6_addr *sender, unsigned char *packet, char *interface);