Keep parent mle_entry in child_update_req timeout (#1693)

When end device fails to attach to new partition it will return back
to old partition. End device is not allowed to delete its parent
mle_entry when parent has moved to new partition and attach fails.

Author: Arto Kinnunen

source/6LoWPAN/Thread/thread_host_bootstrap.c

@@ -890,7 +890,7 @@ static void thread_mle_child_request_receive_cb(int8_t interface_id, mle_message
             break;
         }
         default:
-            tr_debug("Unsupported TLV %d", mle_msg->message_type);
+            tr_debug("Skip msg type %d", mle_msg->message_type);
             break;
 
     }
@@ -998,7 +998,7 @@ static bool thread_child_id_req_timeout(int8_t interface_id, uint16_t msgId, boo
     cur->thread_info->thread_attach_scanned_parent->child_id_request_id = 0;
 
     uint8_t *addr = mle_service_get_msg_destination_address_pointer(msgId);
-    tr_debug("Child ID Request timed out, address: %s", trace_ipv6(addr));
+    tr_debug("Child ID Request timed out: %s", trace_ipv6(addr));
 
     blacklist_update(addr, false);
 
@@ -1023,7 +1023,8 @@ static bool thread_child_id_req_timeout(int8_t interface_id, uint16_t msgId, boo
         ll64[8] ^= 2;
 
         entry_temp = mle_class_get_entry_by_ll64(cur->id, scanned_parent->linkMarginToParent, ll64, false, NULL);
-        if (entry_temp) {
+        if (entry_temp && !thread_check_is_this_my_parent(cur, entry_temp)) {
+            // remove scanned_parent entry only if it is not my parent
             mle_class_remove_entry(cur->id, entry_temp);
         }
     }