linuxkpi: Add `hrtimer_setup()`

[dumbbell]

Summary

hrtimer_setup() replaces hrtimer_init() in Linux 6.15. The API and the role are the same, except:

• it takes the function callback as argument
• if function is NULL, it assigns a default callback

Sponsored by: The FreeBSD Foundation

[bz]

sys/compat/linuxkpi/common/include/linux/hrtimer.h

58

Does that mean this is LINUXKPI_VERSION < 61500? We should probably start hiding this (in a separate pass) to not run into similar problems as we did with, e.g., https://reviews.freebsd.org/D58834, carrying old stuff around endlessly.

67

I know it's weird given everything in here is linux_, but can we call new stuff linuxkpi_ and no longer linux_ ?

sys/compat/linuxkpi/common/src/linux_hrtimer.c

108

This is actually exposed on Linux (probably shouldn't have been there either). Want to call it linuxkpi_hrtimer_dummy_timeout so we could make it public in the future and document that it is a public KPI?

[dumbbell]

Address feedback from @bz.

[dumbbell]

Fix build failure

[bz]

sys/compat/linuxkpi/common/src/linux_hrtimer.c

109

__unused but I am fine even without it of if you just add ti before commit.

[dumbbell]

Add __unused after unused arguent in linuxkpi_hrtimer_dummy_timeout() as suggested by @bz.