Mixer logic improvements

[Teebor-Choka]

Currently the mixer uses the async executor to schedule the packet mixing. A better, more efficient approach is needed, that would in ideal case use a common buffer for outgoing and forwarded packets.

Such a buffer could be used for generating also the looping traffic (e.g. probing path observing), junk traffic (to increase the ambiguity of packet sending for low throughput state of the network) and real mixed packets.

Combining multiple sources and increasing throughput however strains the executor. A better approach would be to use the desired distribution on the output and use tick based sampling in discrete time instances to extract the desired number of packets from an easily poppable buffer.

Description

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Relevant issues

None

Definition of DONE

The mixer working efficiently over:

1. a common buffer
2. using the executor only for single discrete time based wakeups
3. implements true Poisson mixing (Closes Implement Poisson mixing #2549 )