chanfitness: switch to query by channel outpoint

In this commit, the channelEventStore in the channel
fitness subsystem is changed to identify channels
by their outpoint rather than short channel id. This
change is made made becuase outpoints are the preferred
way to expose references over rpc, and easier to perform
queries within lnd.

rpcserver.go

@@ -2852,14 +2852,16 @@ func createRPCOpenChannel(r *rpcServer, graph *channeldb.ChannelGraph,
 		channel.UnsettledBalance += channel.PendingHtlcs[i].Amount
 	}
 
+	outpoint := dbChannel.FundingOutpoint
+
 	// Get the lifespan observed by the channel event store. If the channel is
 	// not known to the channel event store, return early because we cannot
 	// calculate any further uptime information.
-	startTime, endTime, err := r.server.chanEventStore.GetLifespan(channel.ChanId)
+	startTime, endTime, err := r.server.chanEventStore.GetLifespan(outpoint)
 	switch err {
 	case chanfitness.ErrChannelNotFound:
 		rpcsLog.Infof("channel: %v not found by channel event store",
-			channel.ChanId)
+			outpoint)
 
 		return channel, nil
 	case nil:
@@ -2880,7 +2882,7 @@ func createRPCOpenChannel(r *rpcServer, graph *channeldb.ChannelGraph,
 	// channel is known to the event store, so we can return any non-nil error
 	// that occurs.
 	uptime, err := r.server.chanEventStore.GetUptime(
-		channel.ChanId, startTime, endTime,
+		outpoint, startTime, endTime,
 	)
 	if err != nil {
 		return nil, err