mempool: refactor addr index.
mempool: refactor addr index.

decentraland/decentraland-node,VidaID/bcoin,decentraland/decentraland-node,decentraland/bronzeage-node,decentraland/decentraland-node,decentraland/bronzeage-node,VidaID/bcoin,decentraland/bronzeage-node,VidaID/bcoin