ndt7: run tests in a BBR enabled environment

[bassosimone]

As part of merging #24, there is a TODO for myself stating:

/* With old kernels, like the one that we have by default on Travis, there is no support for BBR, which breaks the integration tests. For now we just work around it. TODO(bassosimone): Use docker on travis? */

To which @stephen-soltesz added:

iiuc, We want the integration tests to run a server compiled with full support for BBR even if the tests cannot use bbr.

Adding the #ifdef means that the BBR code does not build or execute at all, right?

iiuc, we want a sufficiently enabled build environment to build successfully without the ifdef and we may allow integration tests in travis or similar that don't use bbr.

Do I understand correctly?

This issue is about further discussing the topic.

[bassosimone]

Unassigning myself as this is not worrying us too much for now. (We are currently using xenial for CI, so this is still an issue, but also a feature 'cause we know we don't depend on BBR.)