L1 DLSCH: don't preallocate memory, improve log

The L1 receives a pointer to the L1 payload to use for PDSCH generation.
This would overwrite an existing pre-allocated pointer. Remove this
preallocation. Instead, allocate it in the simulator (the only place
that actively uses this buffer allocation; in nr-softmodem, it's lost by
assigning a pointer). Allocate with an extra byte, because the payload
(in bits) might not be a multiple of 8 bits/1 byte, so the CRC is in the
last 3 bytes.

Also, improve the log with frame/slot information if the PDSCH payload
pointer is NULL.

openair1/SIMULATION/NR_PHY/dlschsim.c

@@ -497,7 +497,8 @@ int main(int argc, char **argv)
   dlsch0_ue->dlsch_config.tbslbrm = Tbslbrm;
 	printf("harq process ue mcs = %d Qm = %d, symb %d\n", dlsch0_ue->dlsch_config.mcs, dlsch0_ue->dlsch_config.qamModOrder, nb_symb_sch);
 
-	unsigned char *test_input=dlsch->harq_process.pdu;
+  uint8_t test_input[TBS / 8 + 4]; // + 3 for CRC + 1 additional byte, see nr_dlsch_encoding()
+  dlsch->harq_process.pdu = test_input;
 	//unsigned char test_input[TBS / 8]  __attribute__ ((aligned(16)));
 	for (i = 0; i < TBS / 8; i++)
 		test_input[i] = (unsigned char) rand();