Update sys/include/net/nanocoap.h

Co-authored-by: mguetschow <mikolai.guetschow@tu-dresden.de>

sys/include/net/nanocoap.h

@@ -2077,7 +2077,7 @@ ssize_t coap_build_hdr(coap_hdr_t *hdr, unsigned type, const void *token,
  *              was checked to suffice), but may also skip that needless step
  *              if the returned length is less than the requested @p data_length.
  *
- * @return      @p data_len + size of the header written in bytes
+ * @return      @p max_data_len + size of the header written in bytes
  *
  * @retval      0           No response should be sent due to a No-Response option in the request
  * @retval      -ENOSPC     @p rbuf too small