lnonion/trampoline: stop double counting HMAC size

[f321x]

OnionHopsDataSingle.to_bytes() already accounts for the onions hmac internally,
it seems incorrect that we were additionally adding PER_HOP_HMAC_SIZE to the payload
size of the payload returned by .to_bytes().

electrum/electrum/lnonion.py

Lines 76 to 92 in 8e96fef

	def to_bytes(self) -> bytes:
	hmac_ = self.hmac if self.hmac is not None else bytes(PER_HOP_HMAC_SIZE)
	if self._raw_bytes_payload is not None:
	ret = self._raw_bytes_payload
	ret += hmac_
	return ret
	# adding TLV payload. note: legacy hop data format no longer supported.
	payload_fd = io.BytesIO()
	OnionWireSerializer.write_tlv_stream(fd=payload_fd,
	tlv_stream_name=self.tlv_stream_name,
	**self.payload)
	payload_bytes = payload_fd.getvalue()
	with io.BytesIO() as fd:
	fd.write(write_bigsize_int(len(payload_bytes)))
	fd.write(payload_bytes)
	fd.write(hmac_)
	return fd.getvalue()

[SomberNight]

Right.. Yes, that seems to have been a logic bug.