bugfix for phy simulators (not sure if enough)

With the new threading architecture of the UE dlsim
(and others) does not work properly anymore.

When looking at the scope, you see a difference
in PDSCH LLR display. The end is always 0 where
in the current develop branch (tag 2017.w25) it's not.

This commit attempts to fix it.

We still don't have the same behavior as in 2017.w25.
I disabled channel simulation (so that UE RX = eNB TX)
and I have one error where in 2017.w25 I have zero.
For example, here comes the output of a run of "./dlsim":

**********************SNR = 0.000000 dB (tx_lev 51.000000)**************************
Errors (1(0)/1000 0/1 0/0 0/0), Pe = (1.000000e-03,0.000000e+00,-nan,-nan), dci_errors 0/1001, Pe = 0.000000e+00 => effective rate 99.900100, normalized delay 0.001472 (1.001000)

And in 2017.w25 we have (with the same hack to disable
channel simulation):

**********************SNR = 0.000000 dB (tx_lev 51.000000)**************************
Errors (0(0)/1000 0/0 0/0 0/0), Pe = (0.000000e+00,-nan,-nan,-nan), dci_errors 0/1000, Pe = 0.000000e+00 => effective rate 100.000000, normalized delay 0.001471 (1.000000)

There may be a problem somewhere. Or there was one before and we should
have had one error and the new UE architecture fixed things and now
it's as it has to be. Hard to say at this point...

When looking at the scope we quickly see some zeros for the PDSCH
LLR, at the begining this time, not at the end. This is just when
the GUI appears and then all is fine, so this seems to be for the
first frame only. In 2017.w25 this does not happen.

openair1/PHY/INIT/lte_param_init.c

@@ -129,6 +129,9 @@ void lte_param_init(unsigned char N_tx_port_eNB,
 
   UE->perfect_ce = perfect_ce;
 
+  /* the UE code is multi-thread "aware", we need to setup this array */
+  for (i = 0; i < 10; i++) UE->current_thread_id[i] = i % 2;
+
   printf("Done lte_param_init\n");