Adjustments to configib to handle Rocky9 precreated connections

[dubmarm]

The PR is to fix an issue with configib that fails to configure an IB connection if it already exists

The modification include

files altered: xCAT/postscripts/configib

1. Take out a useless segment of arp_ignore and arp_filter that was clearing any sysctl.conf
2. Create a logic to perform nmcli con add if the $nic doesnt exist ELSE perform nmcli con modify
   • Otherwise an error is thrown stating a duplicate con exists with the same name and the adjustments dont occur

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[Obihoernchen]

Please readd arp_ignore and arp_filter. This is needed in IPoIB environments.
But using append/replace is probably a better idea.

[Obihoernchen]

Thank you for this PR!
Can you please sign the CA?
Thank you!