Add package version dependency for point releases

[Florian Eckert]

I would like to add a dependency to mwan3 on a specific kernel version.
In the master branch it does not matter, but I have a use case for this, 
especial for the stable release openwrt-19.07.
I just realized (thanks to @brianjmurrell [1]) that in a stable release, 
this is quite important.

The problem is, that a bug fix has been added to the kernel, which makes 
a workaround in mwan3 superfluous.
This workaround in the mwan3 I have now reverted. Since this is no 
longer needed.
Because of my revert now mwan3 tracking no longer works on IPv6 with 
older kernel version on openwrt-19.07, which do not have at least the 
kernel version from the 19.07.5 point release.
I was also not aware that the packages in the feeds for the point 
release are not pinned to the version that was in the repository when 
the tagging was on.
Only openwrt core is pinned.
The feeds always use the latest stable snapshot builds from 19.07 and so 
are rolling.

The fix now would be to check the version of the kernel when installing 
the package and only install or update the package if the correct 
version is installed.
But how can I do that? This is not a build dependency.

Or does anyone have another suggestion

See discussion on github [2].

Best regards

Florian

[1] https://github.com/brianjmurrell
[2] 
https://github.com/openwrt/packages/commit/6bd3f5c3777c5cbad4ac9156fa5b0fda26af14a9