Linux platform: fix polling queue (#12)

In linux platform, one thread polls for indication
and another thread handle them.
The code to determine the number of free elements in the
queue was buggy resulting in polling too much indication
without being able to store them before dispatching them.

lib/platform/linux/platform.c

@@ -177,18 +177,31 @@ static void * poll_for_indication(void * unused)
         /* Ask for maximum room in buffer queue and less than MAX */
         if (!m_queue_empty && (m_ind_queue_write == m_ind_queue_read))
         {
-            // Queue is FULL
+            // Queue is FULL, wait for POLLING INTERVALL to give some
+            // time for the dispatching thread to handle them
             LOGW("Queue is full, do not poll\n");
+            wait_before_next_polling_ms = POLLING_INTERVAL_MS;
             continue;
         }
         else if (m_queue_empty)
         {
+            // Queue is empty
             free_buffer_room = MAX_NUMBER_INDICATION_QUEUE;
         }
         else
         {
-            free_buffer_room = m_ind_queue_write - m_ind_queue_read % MAX_NUMBER_INDICATION_QUEUE;
+            // Queue has elements, determine the number of free buffers
+            if (m_ind_queue_write > m_ind_queue_read)
+            {
+                free_buffer_room = MAX_NUMBER_INDICATION_QUEUE -
+                                   (m_ind_queue_write - m_ind_queue_read);
+            }
+            else
+            {
+                free_buffer_room = m_ind_queue_read - m_ind_queue_write;
+            }
         }
+
         max_num_indication = free_buffer_room > MAX_NUMBER_INDICATION ?
                                  MAX_NUMBER_INDICATION :
                                  free_buffer_room;