freebsd: ignore IPv6 for now

FreeBSD tun devices don't work with the way we implement IPv6
https://github.com/tailscale/tailscale/issues/1307

At least for now, remove any IPv6 addresses from the netmap.

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

wgengine/router/config_clone.go

@@ -0,0 +1,39 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by tailscale.com/cmd/cloner -type Config; DO NOT EDIT.
+
+package router
+
+import (
+	"inet.af/netaddr"
+	"tailscale.com/types/preftype"
+	"tailscale.com/wgengine/router/dns"
+)
+
+// Clone makes a deep copy of Config.
+// The result aliases no memory with the original.
+func (src *Config) Clone() *Config {
+	if src == nil {
+		return nil
+	}
+	dst := new(Config)
+	*dst = *src
+	dst.LocalAddrs = append(src.LocalAddrs[:0:0], src.LocalAddrs...)
+	dst.Routes = append(src.Routes[:0:0], src.Routes...)
+	dst.DNS = *src.DNS.Clone()
+	dst.SubnetRoutes = append(src.SubnetRoutes[:0:0], src.SubnetRoutes...)
+	return dst
+}
+
+// A compilation failure here means this code must be regenerated, with command:
+//   tailscale.com/cmd/cloner -type Config
+var _ConfigNeedsRegeneration = Config(struct {
+	LocalAddrs       []netaddr.IPPrefix
+	Routes           []netaddr.IPPrefix
+	DNS              dns.Config
+	SubnetRoutes     []netaddr.IPPrefix
+	SNATSubnetRoutes bool
+	NetfilterMode    preftype.NetfilterMode
+}{})