NFD

So, if I'm understanding this issue correctly, the Interest-to-Nack matching function will need to be changed so that all five of the fields match, instead of just the first three as in the Interest-to-Interest matching function?

When forwarder receives a Nack, there are two steps:

1. Locate the PIT entry. This shall consider Name, CanBePrefix, MustBeFresh, and ForwardingHint.
2. Verify that the Nack is against the last forwarded Interest. This shall compare the Nonce in the Nack with the Nonce in the PIT upstream record.

This issue is blocked by #3162 because that issue makes ForwardingHint part of index key in PIT.