Avoid large queries in greylist request

Summary:
The assumption is that the following query can yield a lot of results
for e.g. gmail.com:

$entries = Connect::where(
    [
        'sender_domain' => $this->senderDomain,
        'net_id' => $this->netID,
        'net_type' => $this->netType
    ]
)
    ->whereDate('updated_at', '>=', $this->timestamp->copy()->subDays(7));

Instead of counting and updating all of them, we only to the minimum
work necessary:

• Update all entries that are currently greylisted
• Count if we have at least 5 entries to automatically create a whitelist

This changes that entries that already have greylisting = false will
not get updated_at updated.

Differential Revision: https://git.kolab.org/D2833