I’ve just put the older 4.4 kernel packages in the FlightAware apt repository. If you have this configured (piaware sdcards have this by default) then you can prevent upgrades past 4.4 by creating a file /etc/apt/preferences.d/50-pin-kernel.pref containing this:
Package: raspberrypi-kernel raspberrypi-bootloader libraspberrypi0 libraspberrypi-bin
Pin: origin "flightaware.com"
Pin-Priority: 995
You can check it’s correct via apt-cache policy:
$ sudo apt-get update
$ apt-cache policy raspberrypi-kernel
raspberrypi-kernel:
Installed: 1.20170405-1
Candidate: 1.20170405-1
Package pin: 1.20170405-1
Version table:
1.20170703-1 995
500 http://archive.raspberrypi.org/debian/ jessie/main armhf Packages
*** 1.20170405-1 995
500 http://flightaware.com/adsb/piaware/files/packages/ jessie/piaware armhf Packages
100 /var/lib/dpkg/status
This is probably what I’ll do for the next piaware sdcard release.