gbe_mux, vacc, pack fixes

vacc and pack had misaligned vector lengths causing flushes.
gbe_mux was not inserting gaps correctly between packets causing
overflows in the gbe output fifos.
Full and of counter in gbe no longer go high, correct number of
packets are output (as reported by pack_out_cnt) and no errors
reported by pack block (as reported by pack_out_err).

TODO
* check data output with spead_rx
* software to support other fengine and xengine functionality for RTS
* vacc error debug
* qdr calibration software
* software tidy up
* fft_wideband_real debug