libapi: Add missing header with NAME_MAX define to io_dir.h

Most systems get this indirectly, but some odd cases (some musl libc
systems) can't find it, so just add the header where NAME_MAX is defined
to avoid that.

Fixes: d118b08f ("tools lib api: Add io_dir an allocation free readdir alternative")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20250310194534.265487-2-acme@kernel.org


Signed-off-by: Namhyung Kim <namhyung@kernel.org>