libbpf-cargo: Expose inner Rust "enum" values publicly

With the switch from emitting C enums as Rust enums to mapping them to
Rust structs instead, we no longer allow access to the underlying
integer. That's a bit of a usability snag, because it forces users to
fall back to transmuting constants just to get a hold of the inner
value.
Expose the inner value publicly to make that easier.

Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

libbpf-cargo/src/gen/btf.rs

@@ -810,7 +810,7 @@ impl<'s> GenBtf<'s> {
 
         writeln!(def, r#"#[derive(Debug, Copy, Clone, Eq, PartialEq)]"#)?;
         writeln!(def, r#"#[repr(transparent)]"#)?;
-        writeln!(def, r#"pub struct {enum_name}({signed}{repr_size});"#)?;
+        writeln!(def, r#"pub struct {enum_name}(pub {signed}{repr_size});"#)?;
         writeln!(def, "#[allow(non_upper_case_globals)]")?;
         writeln!(def, r#"impl {enum_name} {{"#,)?;