htlcswitch: add incoming amount and to decode hop iterator request

When we have payments inside of a blinded route, we need to know
the incoming amount to be able to back-calculate the amount that
we need to forward using the forwarding parameters provided in the
blinded route encrypted data. This commit adds the payment amount
to our DecodeHopIteratorRequest so that it can be threaded down to
payment forwarding information creation in later commits.

htlcswitch/link.go

@@ -3160,10 +3160,11 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			onionReader := bytes.NewReader(pd.OnionBlob)
 
 			req := hop.DecodeHopIteratorRequest{
-				OnionReader:   onionReader,
-				RHash:         pd.RHash[:],
-				IncomingCltv:  pd.Timeout,
-				BlindingPoint: pd.BlindingPoint,
+				OnionReader:    onionReader,
+				RHash:          pd.RHash[:],
+				IncomingCltv:   pd.Timeout,
+				IncomingAmount: pd.Amount,
+				BlindingPoint:  pd.BlindingPoint,
 			}
 
 			decodeReqs = append(decodeReqs, req)