ntpd: add SPDX license information

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

net/ntpd/Makefile

@@ -15,6 +15,9 @@ PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=http://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-4.2/
 PKG_MD5SUM:=00df80a84ec9528fcfb09498075525bc
 
+PKG_LICENSE:=Unique
+PKG_LICENSE_FILES:=COPYRIGHT html/copyright.html
+
 PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_VERSION)
 
 PKG_FIXUP:=autoreconf