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

node/node_example_test.go

@@ -22,7 +22,6 @@ import (
 
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/p2p"
-	"github.com/ethereum/go-ethereum/p2p/discover"
 	"github.com/ethereum/go-ethereum/rpc"
 )
 
@@ -42,23 +41,8 @@ func (s *SampleService) Start(*p2p.Server) error   { fmt.Println("Service starti
 func (s *SampleService) Stop() error               { fmt.Println("Service stopping..."); return nil }
 
 func ExampleService() {
-	// Create a network node to run protocols with the default values. The below list
-	// is only used to display each of the configuration options. All of these could
-	// have been omitted if the default behavior is desired.
-	nodeConfig := &node.Config{
-		DataDir:         "",                 // Empty uses ephemeral storage
-		PrivateKey:      nil,                // Nil generates a node key on the fly
-		Name:            "",                 // Any textual node name is allowed
-		NoDiscovery:     false,              // Can disable discovering remote nodes
-		BootstrapNodes:  []*discover.Node{}, // List of bootstrap nodes to use
-		ListenAddr:      ":0",               // Network interface to listen on
-		NAT:             nil,                // UPnP port mapper to use for crossing firewalls
-		Dialer:          nil,                // Custom dialer to use for establishing peer connections
-		NoDial:          false,              // Can prevent this node from dialing out
-		MaxPeers:        0,                  // Number of peers to allow
-		MaxPendingPeers: 0,                  // Number of peers allowed to handshake concurrently
-	}
-	stack, err := node.New(nodeConfig)
+	// Create a network node to run protocols with the default values.
+	stack, err := node.New(&node.Config{})
 	if err != nil {
 		log.Fatalf("Failed to create network node: %v", err)
 	}