Clear IPv6 neighbor cache in partition change (ARMmbed#1554)

Clear IPv6 neighbor cache when moving to new partition in order to
avoid stale cache entries in new partition.

Author: Arto Kinnunen

source/6LoWPAN/Thread/thread_common.c

@@ -1922,12 +1922,19 @@ void thread_mcast_group_change(struct protocol_interface_info_entry *interface,
 
 void thread_old_partition_data_purge(thread_info_t *thread_info)
 {
+    protocol_interface_info_entry_t *cur;
+
     /* Partition has been changed. Wipe out data related to old partition */
     thread_management_client_pending_coap_request_kill(thread_info->interface_id);
 
-    /* Reset/init previous routing information */
+    /* Reset previous routing information */
     thread_routing_reset(&thread_info->routing);
-    thread_routing_init(&thread_info->routing);
+
+    /* Clear previous context ID's */
+    cur = protocol_stack_interface_info_get_by_id(thread_info->interface_id);
+
+    /* Flush address cache */
+    ipv6_neighbour_cache_flush(&cur->ipv6_neighbour_cache);
 }
 
 #endif