I got confused, as we had a struct containing two arrays. Simply expose the
reserve_hop struct and use arrays directly.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
askrene.c was getting quite long, and this is self-contained.
The only code change is a convenience accessor for the per-htlc-cost
hash table.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>