Tidy address-union handling: move class into explicit argument.

This moves the class argument to cache-insert into an argument,
rather then overloading a union in the address argument. Note that
tha class is NOT stored in the cache other than for DS/DNSKEY entries,
so must always be C_IN except for these. The data-extraction code
ensures this as it only attempts to cache C_IN class records.

src/dnsmasq.h

@@ -1144,7 +1144,7 @@ struct crec *cache_find_by_name(struct crec *crecp,
 void cache_end_insert(void);
 void cache_start_insert(void);
 int cache_recv_insert(time_t now, int fd);
-struct crec *cache_insert(char *name, struct all_addr *addr,
+struct crec *cache_insert(char *name, struct all_addr *addr, unsigned short class, 
 			  time_t now, unsigned long ttl, unsigned short flags);
 void cache_reload(void);
 void cache_add_dhcp_entry(char *host_name, int prot, struct all_addr *host_address, time_t ttd);