htlcswitch/link: return FinalFailExpiryTooSoon for last htlc #2335
In this commit, we fix a minor discrepancy with the spec. We should
In this commit, we fix a minor discrepancy with the spec. We should return a FinalFailExpiryTooSoon error, rather than a FinalFailIncorrectCltvExpiry error, when the last HTLC of a route (exit hop) has an expiration height that is deemed too soon by the final destination of the HTLC.