BUG/MINOR: task: make task_instant_wakeup() work on a task not a tasklet

BUG/MINOR: task: make task_instant_wakeup() work on a task not a tasklet

There's a subtle (harmless) bug in task_instant_wakeup(). As it uses
some tasklet code instead of some task code, the debug part also acts
on the tasklet equivalent, and the call_date is only set when DEBUG_TASK
is set instead of inconditionally like with tasks. As such, without this
debugging macro, call dates are not updated for tasks woken this way.

There isn't any impact yet because this function was introduced in 2.6 to
solve certain classes of issues and is not used yet, and in the worst case
it would only affect the reported latency time.

This may be backported to 2.6 in case a future fix would depend on it but
currently will not fix existing code.