Change initial UpLinkCounter values to 0

In LoRaWAN specs (1.0.2), the frame counter is supposed to be reset to 0 on start of APB session. In the code the initial values was 1.
4.3.1.5 Frame counter (FCnt)
 
Lines 21/22 After a JoinReq – JoinAccept message exchange or a reset for a personalized end-device, the frame counters on the end-device and the frame counters on the network server for that end-device are reset to 0.

Author: abouillot

src/mac/LoRaMac.c

@@ -149,7 +149,7 @@ static uint8_t LoRaMacRxPayload[LORAMAC_PHY_MAXPAYLOAD];
  * LoRaMAC frame counter. Each time a packet is sent the counter is incremented.
  * Only the 16 LSB bits are sent
  */
-static uint32_t UpLinkCounter = 1;
+static uint32_t UpLinkCounter = 0;
 
 /*!
  * LoRaMAC frame counter. Each time a packet is received the counter is incremented.
@@ -3012,7 +3012,7 @@ static void ResetMacParameters( void )
     IsLoRaMacNetworkJoined = false;
 
     // Counters
-    UpLinkCounter = 1;
+    UpLinkCounter = 0;
     DownLinkCounter = 0;
     AdrAckCounter = 0;