netsync: ignore tx invs when we're not current

During ibd sometimes we may ban our sync peers because we're attempting
to fetch some txs that may already been confirmed and don't exist in the
mempool anymore.

Since we shouldn't be fetching txs anyways when we're not current, this
commit changes the handleInvMsg logic to ignore tx invs if the node is
not caught up to the tip.

Fixes btcsuite#1984

netsync/manager.go

@@ -1171,6 +1171,11 @@ func (sm *SyncManager) handleInvMsg(imsg *invMsg) {
 		peer.UpdateLastAnnouncedBlock(&invVects[lastBlock].Hash)
 	}
 
+	// Ignore inventory when we're in headers-first mode.
+	if sm.headersFirstMode {
+		return
+	}
+
 	// Ignore invs from peers that aren't the sync if we are not current.
 	// Helps prevent fetching a mass of orphans.
 	if peer != sm.syncPeer && !sm.current() {
@@ -1201,15 +1206,20 @@ func (sm *SyncManager) handleInvMsg(imsg *invMsg) {
 			continue
 		}
 
+		// Ignore txs when we're not current as we can't verify them
+		// and they'll just go in the orphan pool.
+		if iv.Type == wire.InvTypeWitnessTx ||
+			iv.Type == wire.InvTypeTx {
+
+			if !sm.current() {
+				continue
+			}
+		}
+
 		// Add the inventory to the cache of known inventory
 		// for the peer.
 		peer.AddKnownInventory(iv)
 
-		// Ignore inventory when we're in headers-first mode.
-		if sm.headersFirstMode {
-			continue
-		}
-
 		// Request the inventory if we don't already have it.
 		haveInv, err := sm.haveInventory(iv)
 		if err != nil {