The upgrade made the kernel (vmlinuz-4.10.0-37-generic) in which I installed the displaylink driver to be the 3rd in the Grub Advanced Menu. The ordering was automatically generated. For grub to boot this kernel automatically, I put the following directive in /etc/default/grub.
GRUB_DEFAULT="1>2"
The indices of the menus all start at 0.
Thus this default says:
1. select the 2nd line in the top menu (Advanced),
2. descend into the submenu, and then
3. select the 3rd line in the submenu, which is the kernel to which I added the displaylink driver.
I have yet to find a passage in the
grub manual that discusses this usage of GRUB_DEFAULT.
Update
I found where in the manual navigating submenus with GRUB_DEFAULT is almost discussed:
15.1.10 default.