main: Use ast_strdup instead of strdup

Fix compile error in main/utils.c because strdup was used in dummy_start

Change-Id: Id61a6cf4f3cbf235450441e10e7da101a6335793

main/utils.c

@@ -1213,7 +1213,7 @@ static void *dummy_start(void *data)
 
 	lock_info->thread_id = pthread_self();
 	lock_info->lwp = ast_get_tid();
-	lock_info->thread_name = strdup(a.name);
+	lock_info->thread_name = ast_strdup(a.name);
 
 	pthread_mutexattr_init(&mutex_attr);
 	pthread_mutexattr_settype(&mutex_attr, AST_MUTEX_KIND);