[BUG] exclude range currently does not correctly handle invalid syntax

[andreaskaris]

Describe the bug
Invalid syntax in an exclude range is currently ignored, and a nil pointer is added to excludeRanges, leading to a nil pointer exception in skipExludedSubnets
This also includes cases where the excludeRange is a single IP address

Expected behavior
A clear and concise description of what you expected to happen.

To Reproduce
Steps to reproduce the behavior:

1. See the unit tests for the submitted patch

Environment:

• Whereabouts version : N/A
• Kubernetes version (use kubectl version): N/A
• Network-attachment-definition: N/A
• Whereabouts configuration (on the host): N/A
• OS (e.g. from /etc/os-release): N/A
• Kernel (e.g. uname -a): N/A
• Others: N/A

Additional info / context
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