vm_fault: move FAULT_* return codes out of range for Mach errors

[kib]

Summary

This way a possible clash between FAULT_* and KERN_* numbering is
avoided, and panics checks for fault_status confusion become more
efficient.

[markj]

and panics checks for fault_status confusion become more efficient.

I'm not sure what you mean here?

[kib]

In D40771#927711, @markj wrote:

and panics checks for fault_status confusion become more efficient.

I'm not sure what you mean here?

switches with the key by fault_status enum or Mach error have the default: case with panic. If code confuses the enum with Mach error, now it should reliably hit the panic case instead of randomly interpret the value from different namespace.