Notify user of data value change about p-net

[Svenson12]

I had a simmilar requirement. Here what I added to the stack:
I replaced pf_cpm_put_buf as follows:
`
static void pf_cpm_put_buf(
pnet_t *net,
pf_iocr_t *p_iocr,
os_buf_t **pp_buf)
{
pf_cpm_t *p_cpm = &p_iocr->cpm;
pf_iodata_object_t *p_iodata;
const uint8_t *p_old_buffer;
const uint8_t *p_new_buffer;
size_t ix;
void *p;

os_mutex_lock(net->cpm_buf_lock);
p = p_cpm->p_buffer_cpm;
p_cpm->p_buffer_cpm = *pp_buf;
*pp_buf = p;

if ((net->fspm_cfg.change_cb != NULL) &&
(pp_buf != NULL))
{
/ get pointer to new data buffer /
p_new_buffer = &((uint8_t)(p_cpm->p_buffer_cpm->payload))[p_cpm->buffer_pos];

  /* get pointer to old data buffer */
  if ((p_cpm->new_buf == TRUE) || (p_cpm->p_buffer_app == NULL))
  {
     p_old_buffer = &((uint8_t*)((*pp_buf)->payload))[p_cpm->buffer_pos];
  } else
  {
     p_old_buffer = &((uint8_t*)(p_cpm->p_buffer_app->payload))[p_cpm->buffer_pos];
  }

  /* compare content */
  for (ix = 0u; ix < p_iocr->nbr_data_desc; ix++)
  {
     p_iodata = &p_iocr->data_desc[ix];

     if ((p_iodata->in_use == TRUE) &&
         (p_iodata->data_length > 0) &&
         (memcmp (&p_new_buffer[p_iodata->data_offset],
                  &p_old_buffer[p_iodata->data_offset],
                  p_iodata->data_length) != 0))
     {
        /* call callback */
        net->fspm_cfg.change_cb (net, net->fspm_cfg.cb_arg, p_iodata->api_id,
                                 p_iodata->slot_nbr, p_iodata->subslot_nbr);
     }
  }

}

p_cpm->new_buf = TRUE;
os_mutex_unlock(net->cpm_buf_lock);
}
`

In pf_cpm_c_data_ind I call the replaced function now as follows:
pf_cpm_put_buf(net, p_iocr, &p_buf);

In pf_cpm_t I redefined p_buffer_app and p_buffer_cpm as os_buf_t* instead void*.

In pnet_cfg_t I added a new call back:
pnet_change_ind change_cb;
with
typedef int (*pnet_change_ind)( pnet_t *net, void *arg, uint32_t api, uint16_t slot, uint16_t subslot);

In my application I set a flag in the callback function that is handled later on.

[Svenson12]

An additional comment: Some callback functions have the parameter api defined as uint16_t, some as uint32_t. I would say, all should be uint32_t.

[pyhys]

Thanks for your feedback. We will put it in the backlog.
(According to the standard 5.2.4.1 Coding of the field API = Unsigned32)

[pyhys]

Thanks for your very valuable feedback, as always @Svenson12 ! Please review #113