Comment 2 for bug 1682437

Install yakkety in an Ubuntu KVM with two network interfaces.
Enabled yakkety-proposed, did apt full-upgrade.
Executed do-release-upgrade.
It upgraded to zesty, including zesty-proposed.
At the end of do-release-upgrade accepted to reboot.
After reboot, the system come up fine, with network interface names preserved as eth0 and eht1, with networking correctly operating.
Removed /etc/udev/rules.d/70-persistent-net.rules and updated /etc/networking/interfaces to use enc1 (checked that this is the correct persistent name for eth0 using udevadm info -p /sys/class/net/eth0).
Updated initramfs and rebooted.
Still have networking, and now both interfaces use the stable device names enc1 and enc2.