xbee: disable short address when the address length is set to 8

XBee sends short address even for `API_ID_TX_LONG_ADDR` if short address is
enabled. This results in check sum error of ICMPv6 since the IP address is
computed based on long address on the sender side while it is computed based on
short address on the receiver side.

drivers/xbee/xbee.c

@@ -254,31 +254,41 @@ static int _get_addr_long(xbee_t *dev, uint8_t *val, size_t len)
     return -ECANCELED;
 }
 
-static int _set_addr(xbee_t *dev, uint8_t *val, size_t len)
+static int _set_short_addr(xbee_t *dev, uint8_t *address)
 {
     uint8_t cmd[4];
     resp_t resp;
 
+    cmd[0] = 'M';
+    cmd[1] = 'Y';
+    cmd[2] = address[0];
+    cmd[3] = address[1];
+    _api_at_cmd(dev, cmd, 4, &resp);
+
+    return resp.status;
+}
+
+static int _set_addr(xbee_t *dev, uint8_t *val, size_t len)
+{
     /* device only supports setting the short address */
     if (len != 2) {
         return -ENOTSUP;
     }
-    cmd[0] = 'M';
-    cmd[1] = 'Y';
-    cmd[2] = val[0];
-    cmd[3] = val[1];
+
+    if (dev->addr_flags & XBEE_ADDR_FLAGS_LONG ||
+          _set_short_addr(dev, val) == 0) {
 
 #ifdef MODULE_SIXLOWPAN
-    /* https://tools.ietf.org/html/rfc4944#section-12 requires the first bit to
-     * 0 for unicast addresses */
-    val[1] &= 0x7F;
+        /* https://tools.ietf.org/html/rfc4944#section-12 requires the first bit
+         * to 0 for unicast addresses */
+        val[1] &= 0x7F;
 #endif
 
-    _api_at_cmd(dev, cmd, 4, &resp);
-    if (resp.status == 0) {
         memcpy(dev->addr_short, val, 2);
+
         return 2;
     }
+
     return -ECANCELED;
 }
 
@@ -291,9 +301,19 @@ static int _set_addr_len(xbee_t *dev, uint16_t *val, size_t len)
     switch (*val) {
         case 8:
             dev->addr_flags |= XBEE_ADDR_FLAGS_LONG;
+
+            // disable short address
+            uint8_t disabled_addr[] = { 0xFF, 0xFF };
+
+            _set_short_addr(dev, disabled_addr);
+
             break;
         case 2:
             dev->addr_flags &= ~XBEE_ADDR_FLAGS_LONG;
+
+            // restore short address
+            _set_short_addr(dev, dev->addr_short);
+
             break;
         default:
             return -EINVAL;
@@ -771,8 +791,8 @@ static void _isr_event(gnrc_netdev_t *netdev, uint32_t event_type)
     DEBUG(", options: %02x", (uint8_t) dev->rx_buf[1 + addr_len + 1]); // API ID + source address + RSSI
     DEBUG(", payload:");
 
-    for (size_t i = 0; i < dev->rx_limit - pos - 1; i++) {
-        DEBUG(" %02x", (uint8_t) dev->rx_buf[pos + i]);
+    for (size_t i = 0; i < pkt->size; i++) {
+        DEBUG(" %02x", ((uint8_t *) pkt->data)[i]);
     }
     DEBUG("\n");
 #endif