tests/9p: Test `Tsetattr` can truncate unlinked file

Enhance the `use-after-unlink` test with a new check for the
case where the client wants to alter the size of an unlinked
file for which it still has an active fid.

Suggested-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20250312152933.383967-7-groug@kaod.org>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
1 file changed