This change expands the NTP-TZ-DST example to list the active
SNTP servers. It lists the IP address server name (if used) and
reachability in ntpq style octal format.
Tests:
- Build against all LwIP stack configurations and correct
operation with a single SNTP server
- Vary connectivity to an SNTP server and check reachability
updates
- Configure 3 SNTP servers by name
- With a patched LwIP stack that supports simultaneous DHCP
and DHCPv6 SNTP servers check that all server details are
listed and update correctly during operation
d3debb64c9