Fix fault_type handling in vm_map_lookup().

Suppose that the map entry is wired, so that we later assign
fault_type = entry->protection. Suppose further that we jump back to
RetryLookup. Then fault_type will no longer contain the original
fault protection mask, but instead that of the wired entry.

Submitted by: Wuyang Chung <wuyang.chung1@gmail.com>
Reviewed by: kib
MFC after: 3 days
Github PR: https://github.com/freebsd/freebsd/pull/419
Differential Revision: https://reviews.freebsd.org/D22683