Missing linux-modules-extra

[Peter Sabaini]

# Expected behaviour

When configuring a target kernel version we want to install the corresponding linux-image but also linux-modules-extra

# Actual behaviour

If the configured kernel is already active we do not get linux-modules-extra

# Steps to repro

* Bring up a machine

* Install linux-image-X.Y and ensure linux-modules-extra-X.Y isn't installed

* Add a sysconfig unit

* Configure a desired kernel version X.Y on the charm

* Observe: we don't get linux-modules-extra

# Details

When configuring a target kernel version the charm checks if this work is actually necessary (to possibly save a reboot). However this checks the running kernel, so if the kernel is already at the target version we also skip the extra modules install.

I'd propose to split out a check for linux-modules-extra and install that in any case.