lnwire+channeldb: parse inbound fees

In this commit, the tlv extension of a channel update message is parsed.
If an inbound fee schedule is encountered, it is reported in the
graph rpc calls.

routing/router.go

@@ -2763,6 +2763,7 @@ func (r *ChannelRouter) applyChannelUpdate(msg *lnwire.ChannelUpdate) bool {
 		MaxHTLC:                   msg.HtlcMaximumMsat,
 		FeeBaseMSat:               lnwire.MilliSatoshi(msg.BaseFee),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(msg.FeeRate),
+		ExtraOpaqueData:           msg.ExtraOpaqueData,
 	})
 	if err != nil && !IsError(err, ErrIgnored, ErrOutdated) {
 		log.Errorf("Unable to apply channel update: %v", err)