l-tag is not working

[simotuki11]

The following is about the verification process.

Even if the l-tag is specified in the AMS header in sealing process, validation according to the l-tag content is not performed, and the result is fail.

When sealing the ARC, we set l=16, then added a character to the 17th character of the message body and sent the email.
The verification on the receiving side resulted in a fail.

For reference, when I performed the verification using Perl's Mail::DKIM::ARC::Verifier library, the result passed as expected.

[flowerysong]

flowerysong/OpenARC#20 might fix this, but I haven't actually come up with a way to test it yet so it also might not.