Handle IPv4 interface-address labels in Linux.

src/dnsmasq.h

@@ -1030,6 +1030,7 @@ void create_bound_listeners(int die);
 int is_dad_listeners(void);
 int iface_check(int family, struct all_addr *addr, char *name, int *auth_dns);
 int loopback_exception(int fd, int family, struct all_addr *addr, char *name);
+int label_exception(int index, int family, struct all_addr *addr);
 int fix_fd(int fd);
 int tcp_interface(int fd, int af);
 struct in_addr get_ifaddr(char *intr);