The instructions also have a "mode=4" example. I've also seen working:But it is beyond my knowledge. I've only ever been able to play around with a bonded connection at one end, I think and that was a long time ago.
You do have one configuration issue as enp3s0 is defined both as a LANIF and EXTIF.
Also, with enp3s0, can I suggest you install the kmod-r8168 and kmod-r8169 drvers then reboot. The r8168 driver works much better than the r8169 with this NIC.