mdns: respond to discovery with the proper pseudo name _services._dns-sd._udp

Closes https://github.com/espressif/esp-idf/issues/4369
Closes IDFGH-2219

components/mdns/mdns.c

@@ -1255,7 +1255,7 @@ static void _mdns_create_answer_from_parsed_packet(mdns_parsed_packet_t * parsed
                 }
             } else if (q->type == MDNS_TYPE_SDPTR) {
                 shared = true;
-                if (!_mdns_alloc_answer(&packet->answers, MDNS_TYPE_PTR, service->service, false, false)) {
+                if (!_mdns_alloc_answer(&packet->answers, MDNS_TYPE_SDPTR, service->service, false, false)) {
                     _mdns_free_tx_packet(packet);
                     return;
                 }