clarify types for rust/pull/44287

[Eh2406]

If rust/pull/44287 lands then cargobomb tells us that this line will have a type ambiguity error, so this is a PR to preemptively prevent that. I couldn't figure why cargobomb thinks it will only have trouble with the one case so I did all the instances of that idiom.

Also you repo is hard to find from crates.io, can you add links to your toml?

[marcelbuesing]

Alternative

// lib.rs
#![feature(type_ascription)]
// msg.rs
    /// Multipart message
    pub fn multipart(&mut self) -> &mut NlMsgHeader {
        self.flags |= Flags::Multi.into(): u16;
        self
    }
// ... same for all the others

Since type_ascriptions is not yet stable, I guess your approach is better.

[marcelbuesing]

@crhino would you mind merging @Eh2406 changes and releasing a new version ?