BgpSessionDataAggregator: fix logic bug

[afk11]

The BgpSessionDataAggregator::getPeers function takes a parameter (?int $asn = null).

The parameter is not currently used, so nothing should be affected by it so far.

The code passes $asn != null into when, and then uses the result of that expression as an ASN in the query

            ->when( $asn != null, function( Builder $q, $asn ) {
                return $q->where( 'cs.autsys', (int) $asn );
            } )

In the closure, $asn is true or false, which when cast to an int is 0 or 1.

Instead we can rely on when to perform the truthiness check (ensure $asn isn't 0 or null), then typehint $asn as an int, and then the query will work as intended.