Added L2TP/IPSec VPN Server Docker Image

Signed-off-by: Teddysun <i@teddysun.com>

docker/l2tp/Dockerfile

@@ -0,0 +1,25 @@
+# Dockerfile for L2TP/IPSec VPN Server
+# Copyright (C) 2018 Teddysun <i@teddysun.com>
+
+FROM debian:stretch
+MAINTAINER Teddysun <i@teddysun.com>
+
+RUN set -ex \
+    && printf "deb http://deb.debian.org/debian sid main" > /etc/apt/sources.list.d/sid.list \
+    && apt-get update \
+    && apt-get -t sid install -y --no-install-recommends libreswan xl2tpd \
+    && apt-get install -y --no-install-recommends wget iproute2 openssl ca-certificates kmod net-tools iptables \
+    && apt-get -y autoremove \
+    && apt-get -y clean \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY ./ipsec /etc/init.d/ipsec
+COPY ./l2tp.sh /usr/bin/l2tp
+COPY ./l2tpctl.sh /usr/bin/l2tpctl
+RUN chmod 755 /etc/init.d/ipsec /usr/bin/l2tp /usr/bin/l2tpctl
+
+VOLUME /lib/modules
+
+EXPOSE 500/udp 4500/udp
+
+CMD [ "/usr/bin/l2tp" ]