tests: Overly elaborate compiler warning workaround

Clang will rightly point out that example_sockaddr_un in socket-test
will get discarded from the compilation unit as it is completely unused.
Put in a couple of lines which of no value other than stopping Clang
from complaining.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>