FYI New Pi Kernel causes dump1090-fa to run much harder

[abcd567]

@Nitr0

found apt-mark to be much simpler

I dont have any experience to use apt-mark hold for linux kernel, but have used it successfully for packages.

@abcd567

## Issue following command to prevent Ubuntu from replacing above
## installed packages by packages from repository during any unattended upgrade.

$ sudo apt-mark hold librtlsdr0 librtlsdr-dev