Dio prefix handler fix

Only Dio from preferred parent cuold affect prefix age clear and remove operation.

Change-Id: I29d1261e77186ffcff515397af27698867c8374e

Author: Juha Heiskanen

source/RPL/rpl_control.c

@@ -690,8 +690,9 @@ static void rpl_control_process_prefix_options(protocol_interface_info_entry_t *
     bool router_addr_set = false;
 
     rpl_neighbour_t *pref_parent = rpl_instance_preferred_parent(instance);
-
-    rpl_dodag_update_unpublished_dio_prefix_start(dodag);
+    if (neighbour == pref_parent) {
+        rpl_dodag_update_unpublished_dio_prefix_start(dodag);
+    }
 
     for (;;) {
         const uint8_t *ptr = rpl_control_find_option(start, end - start, RPL_PREFIX_INFO_OPTION, 30);
@@ -735,8 +736,9 @@ static void rpl_control_process_prefix_options(protocol_interface_info_entry_t *
 
         start = ptr + 32;
     }
-
-    rpl_dodag_update_unpublished_dio_prefix_finish(dodag);
+    if (neighbour == pref_parent) {
+        rpl_dodag_update_unpublished_dio_prefix_finish(dodag);
+    }
 }
 
 void rpl_control_process_prefix_option(prefix_entry_t *prefix, protocol_interface_info_entry_t *cur)