[csl] fix overflow in calculating semiWindow (#6734)
[csl] fix overflow in calculating semiWindow (#6734)

Regarding:
semiWindow = elapsed * (Get<Radio>().GetCslAccuracy() + mCslParentDrift) / 1000000;

Consider that the worst Get<Radio>().GetCslAccuracy() and
mCslParentDrift are both 255, the max of uint32 is 4294967295, so when
elapsed is about 8500000(just 8.5s elapsed since the last CSL sync),
the product of elapsed and (Get<Radio>().GetCslAccuracy() +
mCslParentDrift) will overflow.

This commit changes the type to uint64_t from uint32_t to avoid the
overflow.
jwhui/openthread,openthread/openthread,abtink/openthread,abtink/openthread,srickardti/openthread,jwhui/openthread,openthread/openthread,srickardti/openthread,srickardti/openthread,jwhui/openthread,jwhui/openthread,abtink/openthread,openthread/openthread,abtink/openthread,srickardti/openthread,openthread/openthread