Self adapting to mark or not mark

[z8a]

To manage mark or not mark condition (I've both on the same connection) and without change too much your software I've modified osdp_cp.c (v1.3.0) in this way:

• if (was_empty && rec_bytes > 0) { / Start of message / pd->tstamp = osdp_millis_now(); }

  if (was_empty && (buf[0] != 0xFF)) { memmove(&buf[1], &buf[0], rec_bytes); buf[0] = 0xFF; rec_bytes++; }

  pd->rx_buf_len += rec_bytes;

  if (IS_ENABLED(CONFIG_OSDP_PACKET_TRACE)) {

I think you could do better. I cannot use the CONFIG_OSDP_SKIP_MARK_BYTE switch because I've both the conditions.