Dear Maintainer,

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When using network-manager with a wired connection, it does not remove
the default IPv6 route when running with kernel 4.1 or 4.2.
The Route is removed running under kernel 3.16

It was reproducible on 2 laptops running under debian testing/unstable.

When plugging in the routes are: (using ip -6 r)
2001:1234:1234:1234::/64 dev eth0  proto ra  metric 100
fe80::/64 dev eth0  proto kernel  metric 256
default via fe80::5054:ff:1234:1234 dev eth0  proto static  metric 100
After unplug:
default via fe80::5054:ff:1234:1234 dev eth0  proto static  metric 100

This breaks networking with non-wired connections afterwards (higher metric)

The IPv4 routes are removed cleanly.

Im am using a little executable script as a workaround
=====================================================
File: /etc/network/if-post-down.d/remove_default_route
#! /bin/bash
ip -6 route flush dev $IFACE
=====================================================

Network-manager connection config
=====================================================
File: /etc/NetworkManager/system-connections/Ethernet
[connection]
id=eth0-dhcp
uuid=75c185ce-edf2-4704-99a7-509905ea3782
type=ethernet
interface-name=eth0
permissions=
secondaries=

[ethernet]
duplex=full
mac-address=F0:DE:F1:AB:6C:A1
mac-address-blacklist=

[ipv4]
dns-search=
method=auto

[ipv6]
dns-search=
ip6-privacy=0
method=auto
=====================================================