If vm_fault_hold(9) finds that fs.m is wired, do not free it after a
pager error, leave the page to the wire owner. E.g. the page might be
a part of the invalidated buffer.

Reported and tested by: pho
Reviewed by: alc, markj
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D8197