MINOR: task: move the profiling checks to the called functions not callers

MINOR: task: move the profiling checks to the called functions not callers

The checks on TH_FL_TASK_PROFILING that are used to decide whether or not
to set t->wake_date from now_mono_time() used to be made in callers of
__tasklet_wakeup_on() and __tasklet_wakeup_after(), but not only this
needlessly inflates code by placing this in every caller (~4kB), it also
renders the design fragile since each caller needs to blindly copy-paste
that statement.

Let's move the operation in the callees instead. As a bonus, it allows
to check the flag on the target thread and not on the calling thread
(which was arguably a bug though without a noticeable effect since for
now profiling is for all threads or none).