We're currently using port rebinding in the temporary os_udp test suite, which
will be removed. The rebinding is basically a workaround so that the test suite
is functional until removed.

We need to solidify our DTS port rebinding policy - do we want to rebind and if
so, under what circumstances.

The current considerations are:
1. Don't modify the DUT/server configuration if not explicitly asked. The port
binding could be configurable in which case we could do the rebinding instead
of just checking the right port in the smoke tests (maybe in the smoke tests,
maybe separately beforehand).
2. We want to be able to run both functional and performance tests in one DTS
run. In this case, we must be able to rebind in case we need to use two
different traffic generators which require different drivers (as is the case
with Scapy for functional testing and T-rex/DPDK tgen for performance testing).
This clashes with the requirement for explicit consent for rebinding, but if we
properly document (in all places - the docs, config, code) that func+perf
testing implies DTS can rebind for this purpose, it could be a sensible
exception. The rebinding would be done only twice, once between functional and
performance test cases and once to revert back to original.