in fact it syncs the USRP time to GPS time when available and then derives the SFN from the USRP time.
a side effect is that now SFN does not necessarily start at 0 and this also required other changes
 - initialization of the future_ul_tti_request.
 - fixing a bug in get_samples_per_slot

This reverts commit 5679e4a3.

changes to support 768-point DFT/IDFT, renaming of 768-point DFT for DFT-precoding (4 DFTs per call)

T tracer was not functional anymore. because init_tpools() was called
before T_Config_Init().

The problem was that init_tpools() creates some threads and T_Config_Init()
does call fork() and the child process (which is the one running the
softmodem, the parent process is used to monitor it, this is the design
of the T tracer, maybe to change at some point, it's too complicated) has
no thread after the fork(). The threads created by init_tpools() are gone.
Game over.

In conclusion: T_Config_Init() has to be called very early in the life of
the softmodem, at least before init_tpools().

         Also remove an obsolete sub-pipeline
Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>