If you stiffen your neck to take a punch then you deserve to be knocked out. Because while having a strong neck helps to reduce the whiplash effect that slightly contributes to concussions, it's the IMPACT energy itself that starts the brain moving around in your noggin.
In other words just because your neck doesn't move doesn't mean you brain did not. Additionally, neck exercises don't do anything to inhibit a knockout from a chin shot or stop it's impact from shocking your mandibular ganglion which also ends with a lights out effect.
Rolling with punches is the key to taking shots without damage.