duplicate address handling (ARMmbed#1709)

handling of receipt of duplicate address in same thread network implemented.

Author: deepakvenugopal

source/6LoWPAN/Thread/thread_extension_bbr.c

@@ -824,7 +824,12 @@ static int thread_extension_bbr_dua_cb(int8_t service_id, uint8_t source_address
     entry_keep_alive = false;
     ipv6_route_t *route = thread_bbr_dua_entry_find(this->interface_id, addr_data_ptr);
 
-    if ( route != NULL && route->info.info != NULL) {
+    // new device has generated duplicate dua
+    if (route != NULL && route->info.info != NULL && memcmp(((thread_pbbr_dua_info_t *)route->info.info)->mleid_ptr,ml_eid_ptr,8) != 0) {
+        bbr_status = THREAD_BBR_STATUS_DUA_ALREADY_IN_USE;
+        goto send_response;
+    }
+    if (route != NULL && route->info.info != NULL && memcmp(((thread_pbbr_dua_info_t *)route->info.info)->mleid_ptr,ml_eid_ptr,8) == 0) {
         ((thread_pbbr_dua_info_t *)route->info.info)->last_contact_time = protocol_core_monotonic_time;
         entry_keep_alive = true;
     }