xtables-addons: import from OpenWrt base

This commit moves xtables-addons from
https://github.com/openwrt/openwrt/tree/master/package/network/utils/xtables-addons
into the package feed repository to allow for dependencies on other feed
packages, such as Perl.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>
[fix commit message]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

net/xtables-addons/patches/002-fix-kernel-version-detection.patch

@@ -0,0 +1,11 @@
+--- a/configure.ac
++++ b/configure.ac
+@@ -44,7 +44,7 @@ regular_CFLAGS="-Wall -Waggregate-return
+ 
+ if test -n "$kbuilddir"; then
+ 	AC_MSG_CHECKING([kernel version that we will build against])
+-	krel="$(make -sC "$kbuilddir" M=$PWD kernelrelease | $AWK -v 'FS=[[^0-9.]]' '{print $1; exit}')"
++	krel="$(make -sC "$kbuilddir" M=$PWD kernelversion | $AWK -v 'FS=[[^0-9.]]' '{print $1; exit}')"
+ 	save_IFS="$IFS"
+ 	IFS='.'
+ 	set x $krel