Allow set custom port for NTP server

[babcca]

Hi,
your SntpClient.java has hardcoded NTP port.
https://github.com/lyft/Kronos-Android/blob/master/kronos-java/src/main/java/com/lyft/kronos/internal/ntp/SntpClient.java#L91

Sometimes is useful host custom NTP server on different then well known (blocked) port.

What about parse port for NTP server from host using : as separator and NTP_PORT as fallback?
Define host like host := "hostname[:port]" where hostname is string containing DNS or IP address of target NTP server and optional port for target listening port number.

Right before dns resolve(InetAddress address = dnsResolver.resolve(host);).