Code returns a list of GuestNetworkInterface, documentation claims
GuestNetworkInfo, which doesn't exist.  Fix the documentation.

Fixes: 3424fc9f (qemu-ga: add guest-network-get-interfaces command)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230425064223.820979-3-armbru@redhat.com>