revert "tools/libs/guest: fix max_pfn setting in map_p2m()"

revert "tools/libs/guest: fix max_pfn setting in map_p2m()"

The reasoning for commit 7bd8989ab77b6a ("tools/libs/guest: fix max_pfn
setting in map_p2m()") was wrong.

The max_pfn field in shared_info is misnamed, it has the semantics of
num_pfns, which is hidden at least partially in Linux, as the kernel is
(wrongly) treating it like the highest used pfn in some places.

So revert above commit.

Fixes: 7bd8989ab77b6a ("tools/libs/guest: fix max_pfn setting in map_p2m()")
Signed-off-by: Juergen Gross <jgross@suse.com>