fix: handle LinkNotFound errors on geneve interface list

[fra98]

Description

This PR modifies the ExistGeneveInterface() function to handle LinkNotFound errors from generic errors.
In this way we can distinguish between the two cases and avoid unnecessary deletion and recreation of geneve tunnels in case we get a generic error when listing existing interfaces. In such case, reconcile will return with error, therefore will be retried.

[adamjensenbot]

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[cheina97]

/rebase test=true

[fra98]

/rebase test=true

[fra98]

/merge