freebsd-update: skip special kernel handling for non-host upgrades

[emaste]

Summary

If upgrading other than the root directory via -b or -j (e.g, upgrading
a jail from outside) we may not have a kernel at all. Skip the special
case that adds the GENERIC kernel.

PR: 264075

[jlduran_gmail.com]

Will this affect upgrading poudriere jails with a kernel, see poudriere-jail(8)'s -K?

[emaste]

In D42004#957784, @jlduran_gmail.com wrote:

Will this affect upgrading poudriere jails with a kernel, see poudriere-jail(8)'s -K?

This special case shouldn't be needed at all, I believe. In normal operation we will match /boot/kernel/kernel to the generic kernel component. This is a fallback case to make sure that *some* kernel is installed on the host so that we don't end up unable to boot, if we don't match.