Function check_id_match_helper 

fn check_id_match_helper<T, U>(my_ident: &T, wanted_ident: &U) -> Result<()>
where
    T: HasRelayIds + ?Sized,
    U: HasRelayIds + ?Sized,

If there is any identity in wanted_ident that is not present in my_ident, return a ChanMismatch error.

This is a helper for Channel::check_match and UnverifiedChannel::check_internal.