MEDIUM: connections: Revamp the way idle connections are killed

MEDIUM: connections: Revamp the way idle connections are killed

The original algorithm always killed half the idle connections. This doesn't
take into account the way the load can change. Instead, we now kill half
of the exceeding connections (exceeding connection being the number of
used + idle connections past the last maximum used connections reached).
That way if we reach a peak, we will kill much less, and it'll slowly go back
down when there's less usage.