htlcswitch: modify the HopIterator interface to utilize per-hop payloads
htlcswitch: modify the HopIterator interface to utilize per-hop payloads

This commit modifies the HopIterator interface to allow nodes that
receive incoming HTLC’s to make forwarding decisions based on the
returned peer hop information, rather than just the next hop. With this
change, we can now enforce our routing policy, and reject any HTLC’s
that violate the policy.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,AndrewSamokhvalov/lnd,aakselrod/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,ddustin/lnd