mdns: update mdns_out_question_s to be in line with mdns_parsed_question_s struct

Closes  espressif/esp-idf#1568


* Original commit: espressif/esp-idf@eddd5c4

Author: david-cermak

components/mdns/private_include/mdns_private.h

@@ -260,7 +260,7 @@ typedef struct mdns_srv_item_s {
 typedef struct mdns_out_question_s {
     struct mdns_out_question_s * next;
     uint16_t type;
-    uint8_t unicast;
+    bool unicast;
     const char * host;
     const char * service;
     const char * proto;