<?php

$myArray = [
  '1.1' => 'INTEGER: 1',    
  '1.2' => 'INTEGER: 2',    
  '1.3' => 'INTEGER: 3',    
  '1.4' => 'INTEGER: 4',    
  '1.5' => 'INTEGER: 5',    
  '1.6' => 'INTEGER: 6',    
  '2.1' => 'STRING: lo',    
  '2.2' => 'STRING: eth0',    
  '2.3' => 'STRING: eth1',    
  '2.4' => 'STRING: wifi0',    
  '2.5' => 'STRING: ath0',    
  '2.6' => 'STRING: br0',
  '3.1' => 'INTEGER: softwareLoopback(24)',
  '3.2' => 'INTEGER: ethernetCsmacd(6)',  
  '3.3' => 'INTEGER: ethernetCsmacd(6)',  
  '3.4' => 'INTEGER: ethernetCsmacd(6)',  
  '3.5' => 'INTEGER: ethernetCsmacd(6)',    
  '3.6' => 'INTEGER: ethernetCsmacd(6)',
];

$newArray = call_user_func_array(
    'array_map',
    array_merge(
        array(NULL),
        array_chunk($myArray, 6)
    )
);
var_dump($newArray);