When starting bootstrap clear candidate parent list

This caused all information to be present when bootstrap was
started

Author: Mika Tervonen

source/6LoWPAN/ws/ws_bootstrap.c

@@ -2229,6 +2229,9 @@ static void ws_bootstrap_start_discovery(protocol_interface_info_entry_t *cur)
     // Clear learned neighbours
     ws_bootstrap_neighbor_list_clean(cur);
 
+    // Clear learned candidate parents
+    ws_bootstrap_candidate_table_reset(cur);
+
     // Clear RPL information
     rpl_control_free_domain_instances_from_interface(cur);
     // Clear EAPOL relay address