Identify failing node by its index

[thomash-acinq]

When a HTLC is failed remotely, the failing node was previously identified by its node id. However this is not enough if the same node appears multiple times in the payment route, for instance for circular rebalancing. We now identify the failing node using its index in the payment route.

[rorp]

👍

"could not decrypt failure onion" errors were pretty annoying.