mobile: register filter APIs (ethereum#25642)

This fixes a regression introduced in PR ethereum#25459.

mobile/geth.go

@@ -27,6 +27,7 @@ import (
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/eth/downloader"
 	"github.com/ethereum/go-ethereum/eth/ethconfig"
+	"github.com/ethereum/go-ethereum/eth/filters"
 	"github.com/ethereum/go-ethereum/ethclient"
 	"github.com/ethereum/go-ethereum/ethstats"
 	"github.com/ethereum/go-ethereum/internal/debug"
@@ -35,6 +36,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p"
 	"github.com/ethereum/go-ethereum/p2p/nat"
 	"github.com/ethereum/go-ethereum/params"
+	"github.com/ethereum/go-ethereum/rpc"
 )
 
 // NodeConfig represents the collection of configuration values to fine tune the Geth
@@ -200,6 +202,14 @@ func NewNode(datadir string, config *NodeConfig) (stack *Node, _ error) {
 			rawStack.Close()
 			return nil, fmt.Errorf("ethereum init: %v", err)
 		}
+		// Register log filter RPC API.
+		filterSystem := filters.NewFilterSystem(lesBackend.ApiBackend, filters.Config{
+			LogCacheSize: ethConf.FilterLogCacheSize,
+		})
+		rawStack.RegisterAPIs([]rpc.API{{
+			Namespace: "eth",
+			Service:   filters.NewFilterAPI(filterSystem, true),
+		}})
 		// If netstats reporting is requested, do it
 		if config.EthereumNetStats != "" {
 			if err := ethstats.New(rawStack, lesBackend.ApiBackend, lesBackend.Engine(), config.EthereumNetStats); err != nil {