srsUE: Fix for NAS overflow counter computation.

srsue/src/stack/upper/nas.cc

@@ -246,8 +246,7 @@ nas::nas(srslte::task_handler_interface* task_handler_) :
   t3421(task_handler_->get_unique_timer()),
   reattach_timer(task_handler_->get_unique_timer()),
   nas_log{"NAS"}
-{
-}
+{}
 
 void nas::init(usim_interface_nas* usim_, rrc_interface_nas* rrc_, gw_interface_nas* gw_, const nas_args_t& cfg_)
 {
@@ -823,7 +822,7 @@ bool nas::integrity_check(byte_buffer_t* pdu)
     uint8_t* mac        = &pdu->msg[1];
 
     // generate expected MAC
-    uint32_t count_est = (ctxt.rx_count & 0x0FF0u) | pdu->msg[5];
+    uint32_t count_est = (ctxt.rx_count & 0x00FFFF00u) | pdu->msg[5];
     integrity_generate(
         &k_nas_int[16], count_est, SECURITY_DIRECTION_DOWNLINK, &pdu->msg[5], pdu->N_bytes - 5, &exp_mac[0]);