Comment 0 for bug 1713142

[Impact]
Backport features in upstream netplan / netplan in artful to zesty, xenial.

[Test cases]

== Autopkgtests ==
Run autopkgtests, they should all pass.

== MTU settings ==
1) Set a MTU for a device managed by NetworkManager:

ethernet:
  eth0:
    renderer: NetworkManager
    mtu: 1400
    dhcp4: yes

2) Verify that the MTU is properly applied to the device.

== IPv6 method=ignore ==
1) Ensure that when no configuration is specified for an interface rendered by NetworkManager, method=ignore is set under [ipv6] in the NetworkManager configuration.

[Regression potential]
Failure to properly configure existing interfaces for MTU settings, IPv6 settings would be regressions; for example, if existing network devices were to all get the same MTU, or the same MTU as another interface configured in netplan although the configuration is not set to apply to them (ie. the config bleeds to other devices); then this would be a regression. Any new failures in autopkgtests would also be regressions to be investigated as possibly caused by the update.