Update Asus-PCE-AC68-AirPort-Extreme.txt

Changed subsystem-id to same as MacPro6,1 which is also using BCM4360 3x3 MIMO Wi-Fi. Use subsystem-id { 0x17, 0x01, 0x00, 0x00 } for 2x2 MIMO Wi-Fi like MacBook Air 2013.