backend not respected when using `--no-restrict` (which is the default)`

[nscottnichols]

Filtering backends with babeltrace_thapi doesn't work with --no-restrict.

${THAPI_ROOT}/bin/babeltrace_thapi trace -b mpi,itt,cxi /path/to/CTF/

The above command still gives all events. This makes some sense, but the usage/help should be updated to document this behavior explicitly if intended.

[TApplencourt]

Now that we have OpenCL + MPI + ITT on the CI at least we will be able to test any fix and regression.

The problem is https://github.com/argonne-lcf/THAPI/blob/572cda4dbea50d24ac85ffb1f00dfae51611a249/utils/babeltrace_thapi.in#L168 we should track some how, from witch backend an event come from.

Or create pluging with if not enable "eat" their event, and then restrcit / no restrict is just for the event not eaten.