MINOR: dns: Maximum DNS udp payload set to 8192

Following up DNS extension introduction, this patch aims at making the
computation of the maximum number of records in DNS response dynamic.
This computation is based on the announced payload size accepted by
HAProxy.
diff --git a/include/proto/dns.h b/include/proto/dns.h
index 5aed46e..aa063c7 100644
--- a/include/proto/dns.h
+++ b/include/proto/dns.h
@@ -33,7 +33,7 @@
 struct task *dns_process_resolve(struct task *t);
 int dns_init_resolvers(int close_socket);
 uint16_t dns_rnd16(void);
-int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, struct dns_resolution *resolution);
+int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, struct dns_resolution *resolution, int max_answer_records);
 int dns_get_ip_from_response(struct dns_response_packet *dns_p,
                              struct dns_options *dns_opts, void *currentip,
                              short currentip_sin_family,