A segmentation fault bug caused by dns-resolver feature

[G-wangd]

1. SYSTEMD is not defined;
2. While run function [system_ip_address_from_str] and function [system_dns_server_set_address] in src/plugins/ietf-system/datastore/running/store.c at Line 360,367 , in func [ system_dns_server_set_address ] server->address.value = strdup(address.value); ,the address.value is null ，this results a segmentation fault;
3. I add address->value = str;after #else in func [system_ip_address_from_str] to solve this question;