5045 use atomic_{inc,dec}_* instead of atomic_add_*

@@ -1682,11 +1682,11 @@
          * atomic decrement the reference count to prevent
          * the race condition with the interrupt thread that
          * is processing a loaned up buffer block.
          */
         free_state = rx_msg_p->free;
-        ref_cnt = atomic_add_32_nv(&rx_msg_p->ref_cnt, -1);
+        ref_cnt = atomic_dec_32_nv(&rx_msg_p->ref_cnt);
         if (!ref_cnt) {
                 atomic_dec_32(&nxge_mblks_pending);
                 buffer = rx_msg_p->buffer;
                 size = rx_msg_p->block_size;
                 NXGE_DEBUG_MSG((NULL, MEM2_CTL, "nxge_freeb: "