add ipv6 to xnet.StackAsync (#107)

* add ipv6 to xnet.StackAsync

* dns improvements

* improve DNS workings of StackAsync

* add tentative ICMPv6

* work on prefixes and fix some small bugs, plan UDP/TCP6

* fix bugs in StackAsync and ipv4.Prefix.Contains

* update arpsubtable

* completely remove legacy internet.StackIP for StackIPv4/v6

* ipv4/ipv6 tcp/udp

* add TCP6/UDP6 dialing APIs

* add xnet.Stack6 interface

* more ipv6 integration into StackAsync; various tweaks to lneto and documentation+TODOs

* add stack6 tests

* replace netip.Prefix with ipv4.Prefix where it makes sense

lneto_test.go

@@ -1,7 +1,9 @@
 package lneto_test
 
 import (
+	"bytes"
 	"math/rand"
+	"os"
 	"testing"
 
 	"github.com/soypat/lneto"
@@ -156,3 +158,17 @@ func TestIPv4TCPChecksum(t *testing.T) {
 		}
 	}
 }
+
+func TestNoDeps(t *testing.T) {
+	data, err := os.ReadFile("go.mod")
+	if err != nil {
+		t.Fatal(err)
+	}
+	const expect = "module github.com/soypat/lneto\n\ngo 1.2"
+	if !bytes.HasPrefix(data, []byte(expect)) {
+		t.Fatalf("unexpected go.mod file:\nexpect:%sx\ngot:%s", expect, string(data))
+	}
+	if bytes.Contains(data, []byte("require")) {
+		t.Fatal("no dependencies allowed in lneto")
+	}
+}