multi: let chan and graph db implement AddrSource

Then use both to construct a multiAddrSource AddrSource and use that
around the code-base.

server.go

@@ -607,12 +607,14 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		HtlcInterceptor:             invoiceHtlcModifier,
 	}
 
+	addrSource := channeldb.NewMultiAddrSource(dbs.ChanStateDB, dbs.GraphDB)
+
 	s := &server{
 		cfg:            cfg,
 		implCfg:        implCfg,
 		graphDB:        dbs.GraphDB.ChannelGraph(),
 		chanStateDB:    dbs.ChanStateDB.ChannelStateDB(),
-		addrSource:     dbs.ChanStateDB,
+		addrSource:     addrSource,
 		miscDB:         dbs.ChanStateDB,
 		invoicesDB:     dbs.InvoiceDB,
 		cc:             cc,
@@ -1629,7 +1631,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 	// static backup of the latest channel state.
 	chanNotifier := &channelNotifier{
 		chanNotifier: s.channelNotifier,
-		addrs:        dbs.ChanStateDB,
+		addrs:        s.addrSource,
 	}
 	backupFile := chanbackup.NewMultiFile(cfg.BackupFilePath)
 	startingChans, err := chanbackup.FetchStaticChanBackups(