fixes for precoding (turning off if nb_antennas_tx=1), configuration files, timing advance with 3/4 sampling on 20 MHz, logging in MAC

bugfix for DCCH2/SRB2 in eNB_scheduler_dlsch.c, demultiplexing SIMD alignment issue in ulsch_decoding.c, IF5 fronthaul modification in lte-enb.c

see issue #43

issue #42

TX as a normal TX

added prach buffer for if4p5 processing in RRU. This fixed a critical bug which was seen for bandwidths greater than 5 MHz.  RRU tested with 5/10 MHz on 1.5 GHz Atom.

tested with both EXMIMO and USRP. performance better than in master branch.