[lwip-devel] Simplify sys_check_core_locking() in contrib/ports/freertos

[Craig McQueen]

For an LWIP_ASSERT_CORE_LOCKED() implementation under FreeRTOS -- in 
contrib/ports/freertos, it looks as though its definition of 
sys_check_core_locking() is more complicated than it needs to be.

There's no need for sys_lock_tcpip_core() etc, for use by LOCK_TCPIP_CORE() 
etc. It's sufficient for sys_mutex_lock() etc to use FreeRTOS recursive mutex, 
and then the default definition of LOCK_TCPIP_CORE() is fine.

sys_check_core_locking() can simply do:

    if ( lwip_tcpip_thread )
    {
        LWIP_ASSERT( "lwip_core_lock", sys_mutex_is_held( &lock_tcpip_core ) );
    }

While sys_mutex_is_held() can be defined as:

bool sys_mutex_is_held( sys_mutex_t *pxMutex )
{
    return ( xSemaphoreGetMutexHolder( *pxMutex ) == 
xTaskGetCurrentTaskHandle() );
}

-- 
Craig McQueen