cmd/geth: add --config file flag (#13875)

* p2p/discover, p2p/discv5: add marshaling methods to Node

* p2p/netutil: make Netlist decodable from TOML

* common/math: encode nil HexOrDecimal256 as 0x0

* cmd/geth: add --config file flag

* cmd/geth: add missing license header

* eth: prettify Config again, fix tests

* eth: use gasprice.Config instead of duplicating its fields

* eth/gasprice: hide nil default from dumpconfig output

* cmd/geth: hide genesis block in dumpconfig output

* node: make tests compile

* console: fix tests

* cmd/geth: make TOML keys look exactly like Go struct fields

* p2p: use discovery by default

This makes the zero Config slightly more useful. It also fixes package
node tests because Node detects reuse of the datadir through the
NodeDatabase.

* cmd/geth: make ethstats URL settable through config file

* cmd/faucet: fix configuration

* cmd/geth: dedup attach tests

* eth: add comment for DefaultConfig

* eth: pass downloader.SyncMode in Config

This removes the FastSync, LightSync flags in favour of a more
general SyncMode flag.

* cmd/utils: remove jitvm flags

* cmd/utils: make mutually exclusive flag error prettier

It now reads:

   Fatal: flags --dev, --testnet can't be used at the same time

* p2p: fix typo

* node: add DefaultConfig, use it for geth

* mobile: add missing NoDiscovery option

* cmd/utils: drop MakeNode

This exposed a couple of places that needed to be updated to use
node.DefaultConfig.

* node: fix typo

* eth: make fast sync the default mode

* cmd/utils: remove IPCApiFlag (unused)

* node: remove default IPC path

Set it in the frontends instead.

* cmd/geth: add --syncmode

* cmd/utils: make --ipcdisable and --ipcpath mutually exclusive

* cmd/utils: don't enable WS, HTTP when setting addr

* cmd/utils: fix --identity

cmd/faucet/faucet.go

@@ -41,11 +41,13 @@ import (
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/eth/downloader"
 	"github.com/ethereum/go-ethereum/ethclient"
 	"github.com/ethereum/go-ethereum/ethstats"
 	"github.com/ethereum/go-ethereum/les"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
+	"github.com/ethereum/go-ethereum/p2p"
 	"github.com/ethereum/go-ethereum/p2p/discover"
 	"github.com/ethereum/go-ethereum/p2p/discv5"
 	"github.com/ethereum/go-ethereum/p2p/nat"
@@ -175,32 +177,29 @@ type faucet struct {
 func newFaucet(genesis *core.Genesis, port int, enodes []*discv5.Node, network int, stats string, ks *keystore.KeyStore, index []byte) (*faucet, error) {
 	// Assemble the raw devp2p protocol stack
 	stack, err := node.New(&node.Config{
-		Name:             "geth",
-		Version:          params.Version,
-		DataDir:          filepath.Join(os.Getenv("HOME"), ".faucet"),
-		NAT:              nat.Any(),
-		DiscoveryV5:      true,
-		ListenAddr:       fmt.Sprintf(":%d", port),
-		DiscoveryV5Addr:  fmt.Sprintf(":%d", port+1),
-		MaxPeers:         25,
-		BootstrapNodesV5: enodes,
+		Name:    "geth",
+		Version: params.Version,
+		DataDir: filepath.Join(os.Getenv("HOME"), ".faucet"),
+		P2P: p2p.Config{
+			NAT:              nat.Any(),
+			NoDiscovery:      true,
+			DiscoveryV5:      true,
+			ListenAddr:       fmt.Sprintf(":%d", port),
+			DiscoveryV5Addr:  fmt.Sprintf(":%d", port+1),
+			MaxPeers:         25,
+			BootstrapNodesV5: enodes,
+		},
 	})
 	if err != nil {
 		return nil, err
 	}
 	// Assemble the Ethereum light client protocol
 	if err := stack.Register(func(ctx *node.ServiceContext) (node.Service, error) {
-		return les.New(ctx, &eth.Config{
-			LightMode:          true,
-			NetworkId:          network,
-			Genesis:            genesis,
-			GasPrice:           big.NewInt(20 * params.Shannon),
-			GpoBlocks:          10,
-			GpoPercentile:      50,
-			EthashCacheDir:     "ethash",
-			EthashCachesInMem:  2,
-			EthashCachesOnDisk: 3,
-		})
+		cfg := eth.DefaultConfig
+		cfg.SyncMode = downloader.LightSync
+		cfg.NetworkId = network
+		cfg.Genesis = genesis
+		return les.New(ctx, &cfg)
 	}); err != nil {
 		return nil, err
 	}