Do not send duplicate data for ntp servers

in the case where multiple network interfaces are present each
interface will return the same ntp server data

Tested: on the system that has multiple eth interfaces

Signed-off-by: Radivoje Jovanovic <radivoje.jovanovic@intel.com>
Change-Id: I642aae7a1c07f7629d696f177ddf326d25e36fb1