Fix NTPServers property in Redfish

Recent changes to phosphor-network have changed the NTPServers property
to be actually StaticNTPServers.  This makes PATCH incorrect.

Tested: Redfish-protocol-validator passes the NTPServers property again.

```
curl -vvvv --insecure --user root:0penBmc https://192.168.7.2/redfish/v1/Managers/bmc/NetworkProtocol

 -X PATCH -d '{"NTP": {"NTPServers": ["time-a-b.nist.gov", "time-b-b.nist.gov"]}}'
```

Now succeeds.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ie4bcfa6190797dd250421d1a512677841a4319e4