Replace to strncmp from strcmp to check device_name on examples/bluetooth/gatt_client

(Amended slightly from version in https://github.com/espressif/esp-idf/pull/502 to
account for differences when adv_name is a prefix of device_name.)

examples/bluetooth/gatt_client/main/gattc_demo.c

@@ -318,8 +318,8 @@ static void esp_gap_cb(esp_gap_ble_cb_event_t event, esp_ble_gap_cb_param_t *par
             }
 
             if (adv_name != NULL) {
-                if (strcmp((char *)adv_name, device_name) == 0) {
-                    ESP_LOGI(GATTC_TAG, "Searched device %s", device_name);
+                if (strlen(device_name) == adv_name_len && strncmp((char *)adv_name, device_name, adv_name_len) == 0) {
+                    ESP_LOGI(GATTC_TAG, "Searched device %s\n", device_name);
                     if (connect == false) {
                         connect = true;
                         ESP_LOGI(GATTC_TAG, "Connect to the remote device.");