message: add repr(C) for ProtocolMagic
diff: @@ -24,6 +24,7 @@ use std::fmt;
  ///
  #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
  #[cfg_attr(feature = "generic-serialization", derive(Serialize, Deserialize))]
  +#[repr(C)]
  pub struct ProtocolMagic(u32);
  impl ProtocolMagic {
  #[deprecated]
  