This change will allow subtypes in wiregen files to have tlvstreams.
Shifting tlv structs above subtypes in header_template is done to prevent
forward declaration.
Since generate-wire prepends 'tlv_' in tlvname, we
have to modify fromwire_subtype_field and towire_subtype_field in
impl_template to accommodate this.
Changelog-Added: This PR would turn our peers into watchtower and enable SCB to create penalty txn.
39f63eb27f