samples/landlock: Add clang-format exceptions

In preparation to a following commit, add clang-format on and
clang-format off stanzas around constant definitions.  This enables to
keep aligned values, which is much more readable than packed
definitions.

Link: https://lore.kernel.org/r/20220506160513.523257-7-mic@digikod.net


Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>