<?php
$weas = [
    [
        'ip_address' => '170.239.86.148',
        'central_report' => 'b.barracudacentral.org',
        'status_ip' => 'blocked',
        'fecha_status' => '2018-01-18',
    ],
    [
        'ip_address' => '186.64.123.67',
        'central_report' => 'b.barracudacentral.org',
        'status_ip' => 'blocked',
        'fecha_status' => '2018-01-18',
    ],
    [
        'ip_address' => '186.64.123.67',
        'central_report' => 'cbl.abuseat.org',
        'status_ip' => 'blocked',
        'fecha_status' => '2018-01-18',
    ],
    [
        'ip_address' => '186.64.123.67',
        'central_report' => 'spam.dnsbl.sorbs.net',
        'status_ip' => 'blocked',
        'fecha_status' => '2018-01-18',
    ]
];

$datos = [];

foreach ($weas as $valor) {
    $ip = $valor['ip_address'];
    $central = $valor['central_report'];

    if (!array_key_exists($ip, $datos)) {
        $datos[$ip]['central'] = [];
    }

    $datos[$ip]['central'][] = $central;
}

var_dump($datos);