emulators/virtualbox-ose-kmod: Fix a pair of VM bugs

• Use vm_pager_allocate() to allocate OBJT_PHYS objects. This ensures that they're initialized properly.
• Don't assume that user wiring will succeed.

This had been a team effort, with multiple independent reports,
a wide variety of experiments, and patches written by kib@
and refined by markj@.

I'm bumping PORTREVISION and aligning the revision of both kmod and
application; it's possible the application bump isn't actually
needed but let's make sure they both get rebuilt with this
important (because of changed kernel assumptions) fix.

PR: 249326
Submitted by: kib, markj
Reported by: adridg, Rainer Hurling
Reviewed by: adridg
Approved by: koobs (vbox)
MFH: 2020Q3