Do not check for iptables module.

[amstewart]

Summary of Changes

The module pre-requisites checks include a check for the iptables
module. As of NILRT 26.8, iptables is no longer installed. And we do not
actually need it for SNAC. So drop the check.

Also make the warning message at the start of nilrt-snac configure a little more noticeable.

Justification

Checking EUID
Checking iptables
modprobe: FATAL: Module ip_tables not found in directory /lib/modules/6.18.37-rt6-g043b43c1079e
iptables v1.8.10 (legacy): can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
(  128) ERROR nilrt_snac.main: Failed to find ip_tables module.

AB#4007929
AB#4022655

Testing

• Installed and ran this build on a NILRT 26.8 VM and confirmed that it no longer attempts to check for iptables.

Procedure

• This PR: changes user-visible behavior, fixes a bug, or impacts the project's security profile; and so it includes a CHANGELOG note.
• I certify that the contents of this pull request complies with the Developer Certificate of Origin.