network data cleared after router forms new partition (ARMmbed#1525)

removed network data from previous leader when router forms own partition.

Author: deepakvenugopal

source/6LoWPAN/Thread/thread_leader_service.c

@@ -1257,6 +1257,9 @@ static int thread_leader_service_leader_init(protocol_interface_info_entry_t *cu
 {
     //Clean All allocated stuff's
     thread_info_t *thread_info = cur->thread_info;
+    // mark and delete previous leader network data information
+    thread_network_data_router_id_mark_delete(&thread_info->networkDataStorage,thread_router_addr_from_id(cur->thread_info->thread_leader_data->leaderRouterId), true);
+    thread_network_data_router_id_free(&thread_info->networkDataStorage, false, cur);
     thread_leader_service_leader_data_free(thread_info);
 
     thread_info->rfc6775 = false;