netann: ignore unknown channel updat on startup

Since the funding manager might be in process of adding the edge to the
graph, we ignore the error.

netann/channel_update.go

@@ -11,6 +11,10 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 )
 
+// ErrUnableToExtractChanUpdate is returned when a channel update cannot be
+// found for one of our active channels.
+var ErrUnableToExtractChanUpdate = fmt.Errorf("unable to extract ChannelUpdate")
+
 // ChannelUpdateModifier is a closure that makes in-place modifications to an
 // lnwire.ChannelUpdate.
 type ChannelUpdateModifier func(*lnwire.ChannelUpdate)
@@ -107,8 +111,7 @@ func ExtractChannelUpdate(ownerPubKey []byte,
 		}
 	}
 
-	return nil, fmt.Errorf("unable to extract ChannelUpdate for channel %v",
-		info.ChannelPoint)
+	return nil, ErrUnableToExtractChanUpdate
 }
 
 // UnsignedChannelUpdateFromEdge reconstructs an unsigned ChannelUpdate from the