unit tests: Only initialise tcpip_adapter() when needed by the test

Prevents unexpected memory allocations when running tests which
don't require tcpip_adapter.

tools/unit-test-app/main/app_main.c

@@ -3,7 +3,6 @@
 #include "freertos/task.h"
 #include "unity.h"
 #include "unity_config.h"
-#include "tcpip_adapter.h"
 
 void unityTask(void *pvParameters)
 {
@@ -13,10 +12,6 @@ void unityTask(void *pvParameters)
 
 void app_main()
 {
-    // TCP/IP adapter is initialized here because it leaks memory so the
-    // initialization in test cases would make the test fail because of leak.
-    tcpip_adapter_init();
-
     // Note: if unpinning this task, change the way run times are calculated in
     // unity_platform
     xTaskCreatePinnedToCore(unityTask, "unityTask", UNITY_FREERTOS_STACK_SIZE, NULL,