les, light: LES/2 protocol version (#14970)

This PR implements the new LES protocol version extensions:

* new and more efficient Merkle proofs reply format (when replying to
  a multiple Merkle proofs request, we just send a single set of trie
  nodes containing all necessary nodes)
* BBT (BloomBitsTrie) works similarly to the existing CHT and contains
  the bloombits search data to speed up log searches
* GetTxStatusMsg returns the inclusion position or the
  pending/queued/unknown state of a transaction referenced by hash
* an optional signature of new block data (number/hash/td) can be
  included in AnnounceMsg to provide an option for "very light
  clients" (mobile/embedded devices) to skip expensive Ethash check
  and accept multiple signatures of somewhat trusted servers (still a
  lot better than trusting a single server completely and retrieving
  everything through RPC). The new client mode is not implemented in
  this PR, just the protocol extension.

eth/backend.go

@@ -54,6 +54,7 @@ type LesServer interface {
 	Start(srvr *p2p.Server)
 	Stop()
 	Protocols() []p2p.Protocol
+	SetBloomBitsIndexer(bbIndexer *core.ChainIndexer)
 }
 
 // Ethereum implements the Ethereum full node service.
@@ -95,6 +96,7 @@ type Ethereum struct {
 
 func (s *Ethereum) AddLesServer(ls LesServer) {
 	s.lesServer = ls
+	ls.SetBloomBitsIndexer(s.bloomIndexer)
 }
 
 // New creates a new Ethereum object (including the
@@ -154,7 +156,7 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 		eth.blockchain.SetHead(compat.RewindTo)
 		core.WriteChainConfig(chainDb, genesisHash, chainConfig)
 	}
-	eth.bloomIndexer.Start(eth.blockchain.CurrentHeader(), eth.blockchain.SubscribeChainEvent)
+	eth.bloomIndexer.Start(eth.blockchain)
 
 	if config.TxPool.Journal != "" {
 		config.TxPool.Journal = ctx.ResolvePath(config.TxPool.Journal)