luci-app-lxc: add spdx license info

Signed-off-by: Luka Perkov <luka@openwrt.org>

utils/luci-app-lxc/Makefile

@@ -10,6 +10,8 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=luci-app-lxc
 PKG_RELEASE:=20141012
 
+PKG_LICENSE:=Apache-2.0
+
 PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)
 
 include $(INCLUDE_DIR)/package.mk