Currently, to compute the 'item' size in a ring buffer, we have
`SIZE32_OF`.
Several issues with this:
- `SIZE32_OF` only works on variables, not types, due to an extra
parenthesis pair. Indeed, `sizeof((int))` is not valid C, whereas
`sizeof((my_var))` is.
- `SIZE32_OF` is not a proper public API
- `SIZE32_OF` rounds down if the argument size is not a multiple
of 4 bytes.
Thus, we introduce a proper `RING_BUF_ITEM_SIZEOF`, fixing the
aforementioned issues.
Signed-off-by: Henri Xavier <datacomos@huawei.com>