lwip: Update AFL host test mock

This commit updates and refactors the AFL host test mock as follows:
- Isolates the mock so that it only relies on lwip component and linux stdlib headers
- Grouped all mock functions in 'esp32_mock.h/c'
- Updates the lwip esp32 port files to include 'esp32_mock.h' when building for linux
- Use host stdlib headers instead of xtensa stdlib headers

components/lwip/test_afl_host/esp32_mock.h

@@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef _ESP32_MOCK_H_
+#define _ESP32_MOCK_H_
+
+#include <stdint.h>
+#include <unistd.h>
+
+/* ------------------------------------------------- ESP32 Port Mock ---------------------------------------------------
+ *
+ * ------------------------------------------------------------------------------------------------------------------ */
+
+// --------------------- lwipopts.h ------------------------
+
+#define ESP_TASK_TCPIP_STACK
+#define ESP_TASK_TCPIP_PRIO
+
+uint32_t esp_random(void);
+
+// --------------------- sys_arch.h ------------------------
+
+// Required to get linux assert.h to work ???
+#define __ASSERT_FUNC __ASSERT_FUNCTION
+
+typedef void * SemaphoreHandle_t;
+typedef void * TaskHandle_t;
+typedef void * QueueHandle_t;
+
+#define vTaskDelay(ms)      usleep((m)*0)
+
+#endif // _ESP32_MOCK_H_