libxtables: use uintmax for xtables_strtoul

Addendum to 2305d5fb42fc059f38fc1bdf53411dbeecdb310b.

I noticed that unsigned long long is not consistently used, for
example, min/max are still just unsigned long, and strtoul is being
called.

Instead of changing it to unsigned long long, just use uintmax
functions right away so this does not need size-related changing in
the future.

Cc: JP Abgrall <jpa@google.com>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
3 files changed