Description
In general, if you're just accepting payment, you shouldn't want to claim HTLCs from channels that already went on-chain - just let the sender retry and make your counterparty pay the on-chain fee rather than us. However, there are some cases where you need to - if you are claiming the HTLC as a part of an on-chain swap, or otherwise forwarded a payment onwards without using the built-in forwarding utilities. Really people probably shoulnd't be doing those things - forwarding should forward the onion for many reasons, swaps should have the on-chain tx go first and then do the lightning bit to avoid channel jamming by accident, but users are probably going to do this anyway, so if we don't support it they'll be annoyed they lost money.
Probably we want this to be a separate claim method, cause normal claims don't want to do this, but we should support it explicitly.