core, eth: split eth package, implement snap protocol (#21482)

This commit splits the eth package, separating the handling of eth and snap protocols. It also includes the capability to run snap sync (https://github.com/ethereum/devp2p/blob/master/caps/snap.md) , but does not enable it by default. 

Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>
Co-authored-by: Martin Holst Swende <martin@swende.se>

tests/fuzzers/rangeproof/debug/main.go

@@ -0,0 +1,41 @@
+// Copyright 2020 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/ethereum/go-ethereum/tests/fuzzers/rangeproof"
+)
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Fprintf(os.Stderr, "Usage: debug <file>\n")
+		fmt.Fprintf(os.Stderr, "Example\n")
+		fmt.Fprintf(os.Stderr, "	$ debug ../crashers/4bbef6857c733a87ecf6fd8b9e7238f65eb9862a\n")
+		os.Exit(1)
+	}
+	crasher := os.Args[1]
+	data, err := ioutil.ReadFile(crasher)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error loading crasher %v: %v", crasher, err)
+		os.Exit(1)
+	}
+	rangeproof.Fuzz(data)
+}