Routing Nodes need a way to announce min-cltv-from-now

[TheBlueMatt]

I've noticed a number of failed payments through my node of late because someone is paying to the next-hop and the invoice (presumably) had a final CLTV of only 14, which hits our "too soon to handle safely" test and we bounce the HTLC. There needs to be, I think, a min_cltv_from_now field in update_channel.

[rustyrussell]

Confused why your node would care about low timeouts on HTLCs it offers? That's your peer's problem, AFAICT. You care about the delta between incoming and outgoing, sure...

[TheBlueMatt]

You also care about the delta from now to the timeout on the inbound edge of the htlc you're forwarding - if its in the past (or soon enough that you can't claim the HTLC on-chain if the outbound edge claims) you should probably not forward the HTLC.

[TheBlueMatt]

But, indeed, that should be covered either way, I think we previously just had an overly aggressive check, sorry for the noise.