the dependency of kernel package should restrict expected version of linux-firmware

[Alex Tu]

Recently, we got a lesson learn from oem issues[1][2] that linux-firmware should always be updated while update kernel package.

The root cause is some kernel update will expect linux-firmware be updated as well.
Users who install new kernel manually could also encounter the same issue that expected firmware is not there to feed new installed kernel.

There's a dependency for linux-firmware in linux-image-generic but not restrict the version.
That means installing new kernel manually will not pull latest linux-firmware as well.

Say, in [2] case, user's system have:
linux-firmware 1.157.4
linux-image 4.4.0-73

Then user install newer kernel by apt-get install, and he will encounter the same error because the newer linux-firmware will not be installed as well.

So for better user experience, the depends of each released linux-image packages should be changed to something like
Depends: linux-firmware (>= 1.157.17)

or to make sure kernel could backward compatible if kernel package not restrict it's linux-firmware dependency.

[1] LP: #1746155
[2] LP: #1764930 , comment #27