Fix a reference count leak in the LinuxKPI due to calling VM open when
it shouldn't be called.

Background:
The Linux VM open operation is called when a new VMA is
created on top of the current VMA. This is done through either mremap
flow or split_vma, usually due to mlock, madvise, munmap and so
on. This is currently not supported by the LinuxKPI.

MFC after: 1 week
Sponsored by: Mellanox Technologies