Keep old kernels
Solution 1:
/etc/kernel/postinst.d/apt-auto-removal generates /etc/apt/apt.conf.d/01autoremove-kernels.
So you can create new file APT configuration file same way.
sudo nano /etc/apt/apt.conf.d/01autoremove-kernels-stop
contains:
APT::NeverAutoRemove
{
"^linux-image-*-generic$";
"^linux-headers-*-generic$";
"^linux-image-extra-*-generic$";
"^linux-signed-image-*-generic$";
"^.*-kernel-*-generic$";
"^linux-tools-*-generic$";
};