The value of sc_tick_now() has microsecond precision, but
sc_cond_timedwait() has only millisecond precision.
To guarantee that sc_tick_now() >= deadline when sc_cond_timedwait()
returns due to timeout, round up to the next millisecond.
This avoids to call a non-blocking sc_cond_timedwait() in a loop for no
reason until a target deadline during up to 1 millisecond.
Refs 682a6911735cb8f6dccd9653ce30b72f267235c6
85edba20e7