eth: fix transaction sender cache miss before broadcast

BroadcastTransactions needs the Sender address to route message
flows from the same Sender address consistently to the same
random subset of peers.
It however spent considerable time calculating Sender the
addresses, even if the Sender address was already calculated and
cached in other parts of the code.

Since we only need the mapping, we can use any signer, and the one
that had already been used is a better choice because of cache reuse.

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

eth/handler.go

@@ -484,7 +484,7 @@ func (h *handler) BroadcastTransactions(txs types.Transactions) {
 	total := new(big.Int).Exp(direct, big.NewInt(2), nil) // Stabilise total peer count a bit based on sqrt peers
 
 	var (
-		signer = types.LatestSignerForChainID(h.chain.Config().ChainID) // Don't care about chain status, we just need *a* sender
+		signer = types.LatestSigner(h.chain.Config()) // Don't care about chain status, we just need *a* sender
 		hasher = crypto.NewKeccakState()
 		hash   = make([]byte, 32)
 	)