linuxkpi: Define hrtimer_try_to_cancel()

It is the same as callout_stop(9) but the return values are different.

Reviewed by: hselasky
Approved by: hselasky
Differential Revision: https://reviews.freebsd.org/D38081

(cherry picked from commit bb651c77f5f71a38dd90b2eee214e7a2224421a7)