xl2tp: add licensing info

[Peter: make license GPLv2 only]
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/xl2tp/xl2tp.mk

@@ -7,6 +7,8 @@
 XL2TP_VERSION = v1.3.1
 XL2TP_SITE = $(call github,xelerance,xl2tpd,$(XL2TP_VERSION))
 XL2TP_DEPENDENCIES = libpcap
+XL2TP_LICENSE = GPLv2
+XL2TP_LICENSE_FILES = LICENSE
 
 define XL2TP_BUILD_CMDS
 	$(SED) 's/ -O2 //' $(@D)/Makefile