The command line to get the error was:
    ./build_oai --eNB -w EXMIMO -c

- some cleanup
- thread names to include UE Mod_id
- arg of UE_thread_rxn_txnp4 to be struct rx_tx_thread_data again
- sync in UE_thread_rxn_txnp4 to use instance_cnt_rxtx again
- UE_thread to call itti_send_msg_to_task with UE->Mod_id + NB_eNB_INST
  instead of INSTANCE_DEFAULT again

This may break the softmodem UE, to be tested.
The most problematic thing may be the synchronization.
I don't think it will impact the processing at all,
but I won't bet my shirt on it.

git show -p 58052152
to see what it's about

git show 157707b0
to see what it's about

This reverts commit ce14050b, reversing
changes made to 0ada1e9e.

oaisim is not functional with several UEs.
This fixes one issue. (It's still not functional for other reasons.)

We should use ENABLE_USE_MME, not USE_MME.
This code is useless anyway (I think, not sure, that's why I
leave it here), because the other threads wait for 'sync_var'
to become >=0.

see issue #166

see issue #165

see issue #165

issue #42

TX as a normal TX