nft-qos: fix include on image build service enable

Fixes: f88485f572 ("nft-qos: silence buildsystem errors")

Prefixing IPKG_INSTROOT to sourced includes is ineffective for this
package.

Source includes only when empty to avoid image make errors.

Signed-off-by: Imran Khan <gururug@gmail.com>

net/nft-qos/files/nft-qos.init

@@ -3,12 +3,14 @@
 # Copyright (C) 2018 rosysong@rosinson.com
 #
 
-. "${IPKG_INSTROOT}/lib/nft-qos/core.sh"
-. "${IPKG_INSTROOT}/lib/nft-qos/monitor.sh"
-. "${IPKG_INSTROOT}/lib/nft-qos/dynamic.sh"
-. "${IPKG_INSTROOT}/lib/nft-qos/static.sh"
-. "${IPKG_INSTROOT}/lib/nft-qos/mac.sh"
-. "${IPKG_INSTROOT}/lib/nft-qos/priority.sh"
+if [ -z "${IPKG_INSTROOT}" ]; then
+	. /lib/nft-qos/core.sh
+	. /lib/nft-qos/monitor.sh
+	. /lib/nft-qos/dynamic.sh
+	. /lib/nft-qos/static.sh
+	. /lib/nft-qos/mac.sh
+	. /lib/nft-qos/priority.sh
+fi
 
 START=99
 USE_PROCD=1