ETX update:

ETX first EPOC is not calculated RSS/LQI for cached etx anymore.
Also If first epoch not RX ACK will be ETX configured MAX.

Change-Id: I00c4fb90243828b9ba746fc01b174af4cc768c67

Author: Juha Heiskanen

source/Service_Libs/etx/etx.c

@@ -92,19 +92,24 @@ static void etx_calculation(etx_storage_t *entry, uint16_t attempts, uint8_t ack
         entry->stored_diff_etx = entry->etx;
     }
 
-
     uint32_t etx = attempts << (12 - ETX_MOVING_AVERAGE_FRACTION);
 
-    if (acks_rx > 1) {
+    if (acks_rx) {
         etx /= acks_rx;
+    } else  {
+        etx = 0xffff;
     }
-
     if ((etx_info.max_etx_update) && etx > etx_info.max_etx_update) {
         etx = etx_info.max_etx_update;
     }
 
-    //Add old etx 7/8 to new one
-    etx += entry->etx - (entry->etx >> ETX_MOVING_AVERAGE_FRACTION);
+    if (etx_info.cache_sample_requested && entry->etx_samples == 1) {
+        // skip the initial value as RSSI generated ETX is not valid
+        etx = etx << 3;
+    } else {
+        //Add old etx 7/8 to new one
+        etx += entry->etx - (entry->etx >> ETX_MOVING_AVERAGE_FRACTION);
+    }
 
     if (etx > 0xffff) {
         etx = 0xffff;