docs: Clarify free_page_reporting attribute
docs: Clarify free_page_reporting attribute

The 'reporting' suffix of the attribute makes it sound like we
could be reporting something to user. While in fact, this is
purely virtio membaloon <-> QEMU business. Clarify the docs to
make it clear.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

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