In this commit, we add a compatibility mode for older version of
clightning to ensure that we're able to properly parse all their channel
updates. An older version of c-lightning would send out encapsulated
onion error message with an additional type byte. This would throw off
our parsing as we didn't expect the type byte, and so we always 2 bytes
off. In order to ensure that we're able to parse these messages and make
adjustments to our path finding, we'll first check to see if the type
byte is there, if so, then we'll snip off two bytes from the front and
continue with parsing. if the bytes aren't found, then we can proceed as
normal and parse the request.
In this commit onion routing error from BOLT#4 have been added, the
initial error construction have been splitted on two parts: The first
part which contains the actual data will reside inside the lnwire
package because it contains all necessary function to decode/encode
the data. The second part obfuscation and hmac checking will resides
inside the lighting-onion package because it requires the key
generation.
