selftests/landlock: Add missing connect(minimal AF_UNSPEC) test

selftests/landlock: Add missing connect(minimal AF_UNSPEC) test

connect_variant(unspec_any0) is called twice. Both calls end
up in connect_variant_addrlen() with an address length of
get_addrlen(minimal=false).
However, the connect() syscall and its variants (e.g.
iouring/compat) accept much shorter addresses of 4 bytes
and that behaviour was not tested.

Replace one of these calls with one using a minimal address
length (just a bare sa_family=AF_UNSPEC field with no actual
address). Also add a call using a truncated address for good
measure.

Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
Link: https://lore.kernel.org/r/20251027190726.626244-3-matthieu@buffet.re
Signed-off-by: Mickaël Salaün <mic@digikod.net>