wgengine/router{win}: ignore broadcast routes added by Windows when removing routes.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/router/router_test.go

@@ -0,0 +1,15 @@
+// Copyright (c) 2021 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.
+
+package router
+
+import "inet.af/netaddr"
+
+func mustCIDRs(ss ...string) []netaddr.IPPrefix {
+	var ret []netaddr.IPPrefix
+	for _, s := range ss {
+		ret = append(ret, netaddr.MustParseIPPrefix(s))
+	}
+	return ret
+}