multi: fix time.Time initialization.

ChanUpdate timestamps are now restircted so that they cannot be
more than two weeks into the future. Moreover channels with both
timestamps in the ReplyChannelRange msg either too far in the past
or too far in the future are not queried.

Moreover fix unitests.

discovery/syncer.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/graph"
 	"github.com/lightningnetwork/lnd/lnpeer"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"golang.org/x/time/rate"
@@ -787,6 +788,16 @@ func isLegacyReplyChannelRange(query *lnwire.QueryChannelRange,
 // reply to the initial range query to discover new channels that it didn't
 // previously know of.
 func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) error {
+	// isStale returns whether the timestamp is too far into the past.
+	isStale := func(timestamp time.Time) bool {
+		return time.Since(timestamp) > graph.DefaultChannelPruneExpiry
+	}
+
+	// isSkewed returns whether the timestamp is too far into the future.
+	isSkewed := func(timestamp time.Time) bool {
+		return time.Until(timestamp) > graph.DefaultChannelPruneExpiry
+	}
+
 	// If we're not communicating with a legacy node, we'll apply some
 	// further constraints on their reply to ensure it satisfies our query.
 	if !isLegacyReplyChannelRange(g.curQueryRangeMsg, msg) {
@@ -838,9 +849,9 @@ func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) erro
 	}
 
 	for i, scid := range msg.ShortChanIDs {
-		info := channeldb.ChannelUpdateInfo{
-			ShortChannelID: scid,
-		}
+		info := channeldb.NewChannelUpdateInfo(
+			scid, time.Time{}, time.Time{},
+		)
 
 		if len(msg.Timestamps) != 0 {
 			t1 := time.Unix(int64(msg.Timestamps[i].Timestamp1), 0)
@@ -848,6 +859,32 @@ func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) erro
 
 			t2 := time.Unix(int64(msg.Timestamps[i].Timestamp2), 0)
 			info.Node2UpdateTimestamp = t2
+
+			// Sort out all channels with outdated or skewed
+			// timestamps. Both timestamps need to be out of
+			// boundaries for us to skip the channel and not query
+			// it later on.
+			switch {
+			case isStale(info.Node1UpdateTimestamp) &&
+				isStale(info.Node2UpdateTimestamp):
+
+				continue
+
+			case isSkewed(info.Node1UpdateTimestamp) &&
+				isSkewed(info.Node2UpdateTimestamp):
+
+				continue
+
+			case isStale(info.Node1UpdateTimestamp) &&
+				isSkewed(info.Node2UpdateTimestamp):
+
+				continue
+
+			case isStale(info.Node2UpdateTimestamp) &&
+				isSkewed(info.Node1UpdateTimestamp):
+
+				continue
+			}
 		}
 
 		g.bufferedChanRangeReplies = append(