les: do not directly import package eth from les

[zsfelfoldi]

This PR does some refactoring in order to remove all imports of package eth from package les (except for api_test which is an end-to-end test). Dependence on the eth package was ugly anyway but the current reason is that eth package imports the tracer which imports duktape which cannot be compiled with CGO and therefore go-fuzz could not fuzz anything in package les.

• eth.Config is moved to package eth/protocols/eth (is that a good place for the config?)
• eth.NewBloomIndexer is moved to package core (the rest of the indexer logic is there anyway)
• eth.CreateConsensusEngine is passed as a function parameter to les.New

[holiman]

Let's use something a bit more friendly, perhaps

Suggested change

	func New(stack *node.Node, config *eth.Config, cc consensusCreatorFn) (*LightEthereum, error) {
	func New(stack *node.Node, config *eth.Config, mkEngineFn consensusCreatorFn) (*LightEthereum, error) {

[zsfelfoldi]

done

[fjl]

The config should probably live in a 'data package' that's shared between les and eth.
The package could be eth/ethconfig. This could also be the place for things like CreateConsensusEngine.