Configures iptables alternatives on specific OS versions

Ensures consistent iptables behavior across CentOS/AlmaLinux/Rocky 8 by switching to the legacy iptables implementation.
These OS versions use nftables by default, which has a different syntax. This change provides a consistent testing environment.

Author: david22swan

spec/spec_helper_acceptance_local.rb

@@ -114,5 +114,11 @@ def fetch_os_name
     # this so that policycoreutils is installed on platform where the os.family fact
     # is set to 'redhat'
     LitmusHelper.instance.run_shell('yum install policycoreutils -y') if ['almalinux-8', 'rocky-8'].include?("#{fetch_os_name}-#{os[:release].to_i}")
+
+    # On CentOS/AlmaLinux/Rocky 8 iptables is just a frontend to nftables
+    # and the syntax is different. Switch to legacy iptables to have a
+    # consistent experience across OS versions.
+    LitmusHelper.instance.run_shell('sudo update-alternatives --set iptables /usr/sbin/iptables-legacy') if ['almalinux-8', 'centos-8', 'rocky-8'].include?("#{fetch_os_name}-#{os[:release].to_i}")
+    LitmusHelper.instance.run_shell('sudo update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy') if ['almalinux-8', 'centos-8', 'rocky-8'].include?("#{fetch_os_name}-#{os[:release].to_i}")
   end
 end