mdns: Fix test_app build

Author: Lapshin

components/mdns/tests/test_apps/CMakeLists.txt

@@ -4,7 +4,7 @@ cmake_minimum_required(VERSION 3.5)
 
 # (Not part of the boilerplate)
 # This example uses an extra component for common functions such as Wi-Fi and Ethernet connection.
-set(EXTRA_COMPONENT_DIRS "../../../../common_components/protocol_examples_common")
+set(EXTRA_COMPONENT_DIRS ../../ ../../../../common_components/protocol_examples_common)
 
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)