Macro impl_dlc_writeable_external_enum 

macro_rules! impl_dlc_writeable_external_enum {
    ($st:ident $(<$gen: ident>)?, $name: ident, $(($variant_id: expr, $variant_name: ident, $variant_mod: ident)), * ) => { ... };
}

Implements the lightning::util::ser::Writeable trait for an enum external to this crate.