rlc_um: reduce log level when provided space is not enough to build PDU

this is not a warning case as it can always happen. reduce level to info therefore.

lib/src/upper/rlc_um_lte.cc

@@ -135,7 +135,7 @@ int rlc_um_lte::rlc_um_lte_tx::build_data_pdu(unique_byte_buffer_t pdu, uint8_t*
   int pdu_space = SRSLTE_MIN(nof_bytes, pdu->get_tailroom());
 
   if (pdu_space <= head_len + 1) {
-    log->warning("%s Cannot build a PDU - %d bytes available, %d bytes required for header\n",
+    log->info("%s Cannot build a PDU - %d bytes available, %d bytes required for header\n",
               rb_name.c_str(),
               nof_bytes,
               head_len);