Use static NTP server configuration

Ignore NTP servers provided via DHCP.
Enable real-time scheduling for Chrony.

sw/buildroot_overlay/etc/chrony.conf

@@ -1,3 +1,4 @@
-include /etc/chrony_dhcp.conf
-pool pool.ntp.org iburst
+sourcedir /etc/chrony/sources.d
 makestep 0.1 3
+sched_priority 1
+cmdport 0

sw/buildroot_overlay/usr/share/udhcpc/default.script.d/ntp_chrony.script

@@ -1,29 +0,0 @@
-#!/bin/sh
-#
-# Configure chrony to use NTP server advertised by DHCP server.
-#
-
-configure_ntp() {
-
-    # Do nothing if the DHCP server does not advertise any NTP server.
-    [ -z "$ntpsrv" ] && return
-
-    # Write config snippet with NTP servers.
-    for srv in $ntpsrv ; do
-        echo "server $srv iburst"
-    done > /etc/chrony_dhcp.conf.new
-
-    # Compare to currently configured NTP servers.
-    if ! diff -q /etc/chrony_dhcp.conf /etc/chrony_dhcp.conf.new >/dev/null ; then
-        # Update configuration and restart Chrony.
-        mv /etc/chrony_dhcp.conf.new /etc/chrony_dhcp.conf
-        /etc/init.d/S49chrony reload
-    fi
-}
-
-case "$1" in
-    renew|bound)
-        configure_ntp
-        ;;
-esac
-