pnet_macros: fix num_bytes calculation

[yu-re-ka]

The following would panic in debug-mode, and produce garbage in release-mode:

#[packet]
pub struct Test {
    banana: u2,
    apple: u4,
    potato: u6,
    the_rest: u20be,
    #[payload]
    payload: Vec<u8>,
}

[stappersg]

Warning: "github" squashes commits by default.

I think the two commits in this merge request should go in two separate commits.

[yu-re-ka]

@mrmonday can you have a look?

[mrmonday]

Could you add your sample struct into pnet_macros/tests/run-pass/ please?

Sorry for the delay.

[mrmonday]

In future, the best way to get my attention is to ping me on IRC (#libpnet on irc.libera.chat) - github notifications have a habit of getting buried in my inbox :)

[yu-re-ka]

Could you add your sample struct into pnet_macros/tests/run-pass/ please?

Done

Sorry for the delay.

A few days are not a problem, if it gets into the weeks we should maybe talk about adding some more maintainers ;)

[mrmonday]

I keep adding new maintainers, they always seem to disappear after a while though...

[mrmonday]

Looks good, thanks!