Restore EPT protection checks on VMX when using VMM_IOC_MPROTECT_EPT

Restore EPT protection checks on VMX when using VMM_IOC_MPROTECT_EPT

A prior fix related to lack of TLB flushing accidentally removed the
fault type checks related to the access protection features available
via the VMM_IOC_MPROTECT_EPT ioctl. This restores the same logic for
checking the fault type and the exit to userland if the fault is due
to EPT access protections.

While here, update the comment for vmx_fault_page to accurately
reflect the various potential return values.

Reported by Adam Steen.

OK mlarkin@