Support Inbound Fees when LND 18 is released.

[ziggie1984]

See for reference:

1. htlcswitch: add inbound routing fees receive support lightningnetwork/lnd#6703
   and
2. routing: inbound fees send support lightningnetwork/lnd#6934

Maybe we also need to wait for the buildroute command as well:

3. router: inbound fees support for BuildRoute lightningnetwork/lnd#7060

[Bitcoinite]

bump this. I recently started using regolancer again and would really like to use the new inbound fee discounts

[rkfg]

I suppose we need lnd to support building such routes first. I'd really suggest against manually doing this because the logic is complex enough and these rules might change in the future. For example, if/when lnd supports total negative inbound fees, that is when you agree to pay for inbound discounting it below zero. This kind of logic should always be on the lnd side.

[feelancer21]

@Bitcoinite What feature are you missing? For inbound discounts I don't see any todos on the regolancer side. QueryRoutes of lnd supports inbound fees, but not BuildRoute. That means when using the rapid rebalancer you can have a situation, that the first payment supports inbound discounts, but the following payments not. But BuildRoute should be fixed with the next lnd version.

lightningnetwork/lnd#8886