changes for oaisim to function with new threading architecture and trx_read/trx_write emulation. Tested for 5/10 MHz TM1. Multiple-antenna mode fails.

usrp 20 MHz on 30.72 master clock. fixed memory leak in prach.c for 20 MHz with 3/4 sampling. added default attributes to threads in lte-enb.c

It creates more problems than it solves.

We replace this approach by a straightforward
synchronous one.

Now in the downlink, at frame f and subframe s
we use HARQ process (f * 10 + s) % 8.
This is similar to uplink scheduling.