zone: improved logging when master is not usable

If the preferred master address fails, emit warning immediately.
When trying the configured masters by the list later, warn about the preferred
master only if it has been tried again (i.e. on another of its addresses).

src/knot/zone/zone.c

@@ -424,6 +424,11 @@ int zone_master_try(conf_t *conf, zone_t *zone, zone_master_cb callback,
 		}
 
 		log_try_addr_error(zone, NULL, &preferred.addr, err_str, ret);
+
+		char addr_str[SOCKADDR_STRLEN] = { 0 };
+		sockaddr_tostr(addr_str, sizeof(addr_str), &preferred.addr);
+		log_zone_warning(zone->name, "%s, address %s not usable",
+		                 err_str, addr_str);
 	}
 
 	/* Try all the other servers. */
@@ -435,6 +440,7 @@ int zone_master_try(conf_t *conf, zone_t *zone, zone_master_cb callback,
 		conf_val_t addr = conf_id_get(conf, C_RMT, C_ADDR, &masters);
 		size_t addr_count = conf_val_count(&addr);
 
+		bool tried = false;
 		for (size_t i = 0; i < addr_count; i++) {
 			conf_remote_t master = conf_remote(conf, &masters, i);
 			if (preferred.addr.ss_family != AF_UNSPEC &&
@@ -443,6 +449,7 @@ int zone_master_try(conf_t *conf, zone_t *zone, zone_master_cb callback,
 				continue;
 			}
 
+			tried = true;
 			int ret = callback(conf, zone, &master, callback_data);
 			if (ret == KNOT_EOK) {
 				success = true;
@@ -453,7 +460,7 @@ int zone_master_try(conf_t *conf, zone_t *zone, zone_master_cb callback,
 			                   err_str, ret);
 		}
 
-		if (!success) {
+		if (!success && tried) {
 			log_zone_warning(zone->name, "%s, remote %s not usable",
 			                 err_str, conf_str(&masters));
 		}