Changed listener to not busy-wait

[AmeliaEScott]

Describe problem solved by the proposed pull request
Under certain circumstances, when running the listener command with the -n argument, it would incorrectly timeout. For example, by using uorb top, I can see that the telemetry_status message is being published once per second. However, when running listener telemetry_status -n 100, I receive two messages, then the message Waited for 2 seconds without a message. Giving up.

Test data / coverage
I ran a series of listener commands on different topics, with every possible combination of the -i, -r, and -n parameters.

Describe your preferred solution
I suspect that the issue had something to do with the listener performing a busy-wait between messages, therefore using up all available CPU. This can be demonstrated by running listener cpuload -n 10 and observing that the load on every message except for the first is 100%. So, I changed the listener to poll on messages asynchronously. This fixed the issue with telemetry_status.

Additional context
Some work has been done recently on the listener, in #12799 and #13006 .

[julianoes]

Nice!