sbin/ipfw: fix parsing error in nat config port_range

[terehovv_mail.ru]

Summary

This patch fixes a port range parsing error.
Unlike the patch from the PR, this patch uses strsep().

PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263240

[terehovv_mail.ru]

Add diff context

[terehovv_mail.ru]

Fix tests for nat:ipfw_portalias

[terehovv_mail.ru]

Added set -e to the test script to ensure it is correct

[lytboris_gmail.com]

Code is fine, some finishing touches are needed.

sbin/ipfw/nat.c

771

I would use base = 0 here, no reason to limit port range to be in decimal form.

772

ipfw.8 must be changed to reflect port range limits:

port_range lower-upper
        Set the aliasing ports between the ranges given.  Upper port has
        to be greater than lower.

[terehovv_mail.ru]

Update ipfw.8 man page
Update strtol() to use base = 0