events are accepted by the logger if the filter accepts them
the filter is optional (no filter means to accept all events)

plus some cleanup here and there

as special events.

If we store all received events to a file, this dump is now
self-contained. Helps to analyze traces.

Some functions have also been factorized in the process, too much
duplication.

(Also tracer/Makefile was forgotten in previous commit, included
in this one...)

- add on/off command line options

only works for 5MHz (7680 samples per TTI), one transport block
(basic FDD thing)