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/port/esp32/include/arch/sys_arch.h

@@ -33,11 +33,14 @@
 #ifndef __SYS_ARCH_H__
 #define __SYS_ARCH_H__
 
+#ifdef __linux__
+#include "esp32_mock.h"
+#else
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 #include "freertos/queue.h"
 #include "freertos/semphr.h"
-#include "arch/vfs_lwip.h"
+#endif // __linux__
 
 #ifdef __cplusplus
 extern "C" {