illumos gate

When walking PCI capabilities, it is possible for something to screw up in a way that you start reading garbage. When this happens, your only hope is that you find a register that actually looks like a proper capability that ends the list. However, this might not happen and an example of that is present in #14193. In pcieadm and others, the amount of iterations if often bounded because there are only so many caps that can fit in either basic or extended configuration space based on the size of the capability.