[source] sysntpd: restore support for peer-less (standalone) mode

[LEDE Commits]

pepe2k pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/a49503bbc75da39a8a2b0a9da0053e7b968b5e8b

commit a49503bbc75da39a8a2b0a9da0053e7b968b5e8b
Author: Piotr Dymacz <pepe2k at gmail.com>
AuthorDate: Mon Mar 6 23:20:37 2017 +0100

    sysntpd: restore support for peer-less (standalone) mode
    
    ntpd from Busybox supports peer-less (standalone) mode when it's started
    with option -l and without any peer provided with option -p. In this
    mode ntpd uses local time as reference and acts as stratum 1 server.
    
    This mode can be used in isolated networks, where Internet access and/or
    other NTP server/s are not available, but the device has some other way
    of getting correct time, like e.g. GPS (ugps supports setting local time
    by default).
    
    Support for this mode was incorrectly disabled/removed in:
    1527f96ca6e196fa17c96fdb3ae520158fa5943f
    
    Signed-off-by: Piotr Dymacz <pepe2k at gmail.com>
    Acked-by: Jo-Philipp Wich <jo at mein.io>
---
 package/utils/busybox/files/sysntpd | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/utils/busybox/files/sysntpd b/package/utils/busybox/files/sysntpd
index 98260be..e693e40 100755
--- a/package/utils/busybox/files/sysntpd
+++ b/package/utils/busybox/files/sysntpd
@@ -45,7 +45,7 @@ start_service() {
 
 	[ $use_dhcp = 1 ] && get_dhcp_ntp_servers "$dhcp_interface"
 
-	[ -z "$server" ] && return
+	[ -z "$server" -a "$enable_server" = "0" ] && return
 
 	procd_open_instance
 	procd_set_param command "$PROG" -n -N