Intel AX200 seems to map other usable address space into the
same page holding the the MSI-X table (which may be against the spec).
Map the host view of MSI-X Table page of the bar and perform
reads/writes on that for anything not covered by the MSI-X PBA or
the MSI-X Table.
Many thanks to grehan and jhb for helping to figure this out.
Sponsored by: The FreeBSD Foundation