Great question — answering as the UphillTech team:
A quote from the handbook: Only the GENERIC kernel can be automatically updated by freebsd-update. If you need a network driver that is not built in the GENERIC kernel, see if it is available as a module and load it automatically from /boot/loader.conf . Then you can stick with GENERIC. If that doesn't work, you'll probably have to do a build from source.
Full answer by Roland Smith: https://superuser.stackexchange.com/a/658045 (CC BY-SA 3.0).
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