initramfs config script mixes IPv4 and IPv6 data in the net-$iface.conf file

[Mathieu Trudel-Lapierre]

[Impact]
To support the previous behavior with ipconfig, dhclient now ships a config script for the initramfs which is meant to write out /run/net-(interface name).conf, which may be read by later initramfs scripts to configure a remote rootfs or other networked features. Data for both IPv4 and IPv6 are written out to the same file, which can lead to confusion and incorrect behavior.

[Test case]
1) Boot a system with an iscsi rootfs on a network where no DHCP server answers.

Current behavior:
dhclient -6 results may be written out to the /run/net-$iface.conf file which would cause the boot process to continue, thinking it's done.

Expected behavior:
boot should only continue once a network is found (through DHCP, BOOTP, etc.).

[Regression potential]
This changes is not expected to cause any kind of regression. Use of isc-dhcp has been reverted in initramfs-tools, and as such the affected code paths would not be run.

[Mathieu Trudel-Lapierre (cyphermox)]

Fixed in zesty:
https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.3-5ubuntu17