NOTE_ABSTIME values are converted to values relative to boottime in
filt_timervalidate(), and negative values are currently rejected. We
don't reject times in the past in general, so clamp this up to 0 as
needed such that the timer fires immediately rather than imposing what
looks like an arbitrary restriction.
Another possible scenario is that the system clock had to be adjusted
by ~minutes or ~hours and we have less than that in terms of uptime,
making a reasonable short-timeout suddenly invalid. Firing it is still
a valid choice in this scenario so that applications can at least
expect a consistent behavior.
(cherry picked from commit 9c999a259f)
(cherry picked from commit 2f4dbe279f)
121740e185