busybox: sysntpd: add trigger to reload server

busybox: sysntpd: add trigger to reload server

sysntpd server becomes unavailable if the index of the bound
interface changes. So let's add an interface trigger to reload sysntpd.

This patch also adds the ability for the sysntpd script to handle
uci interface name from configuration.

Fixes: 4da60500ebd2 ("busybox: sysntpd: option to bind server to iface")
Signed-off-by: Alexey Dobrovolsky <dobrovolskiy.alexey@gmail.com>
Reviewed-by: Philip Prindeville <philipp@redfish-solutions.com>
(cherry picked from commit 88114f617ae7bffe13d19d7b9575659a3d3cd9b6)