Implement mock capture source

[fako1024]

In els0r/goProbe#80 and other places there are already some bits and peaces regarding mock capture sources, something that greatly helps testing and benchmarks alike.
Ideally this would be basic functionality on the lowest level in this package (i.e. a mockable socket that can we wrapped with an actual ring buffer (and depending on the outcome of #4 maybe even for the non-ring source).

DoD

• Provide mock socket and allow wrapping in at least ring buffer source
• Deploy some tests / benchmarks in this package
• Replace parts of the mock capture logic implemented in els0r/goProbe#80

[fako1024]

Raised els0r/goProbe#88 for required changes in goProbe.