Usbip not found for kernel 4.4.143-999

Hi, I was interested in using usbip on the Rock Pi S, but I get this error when trying to run it:

WARNING: usbip not found for kernel 4.4.143-999

You may need to install the following packages for this specific kernel:

You may also want to install one of the following packages to keep up to date:

I am using a custom kernel, built using the supplied instructions. Can anyone advise how to compile linux-tools for the custom kernel?