pgsql: Refactor DetermineSleepTime() to use milliseconds.

Refactor DetermineSleepTime() to use milliseconds.

Since we're not using select() anymore, we don't need to bother with
struct timeval.  We can work directly in milliseconds, which the latch
API wants.

Discussion: https://postgr.es/m/CA%2BhUKG%2BZ-HpOj1JsO9eWUP%2Bar7npSVinsC_npxSy%2BjdOMsx%3DGg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5a26c7b310b629f8893483cc3cce5bbfa7879115

Modified Files
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src/backend/postmaster/postmaster.c | 57 ++++++++++++-------------------------
1 file changed, 18 insertions(+), 39 deletions(-)