Allow Remote port binding

Signed-off-by: Martyn Ranyard <m@rtyn.berlin>

docker/ssh/Dockerfile

@@ -1,7 +1,10 @@
 FROM library/alpine
 RUN apk add --no-cache openssh && \
-  sed -i /etc/ssh/sshd_config -e s/'#Port.*'/'Port 2222'/ -e s/'AllowTcpForwarding.*'/'AllowTcpForwarding yes'/ && \
-  ssh-keygen -A
+  sed -i /etc/ssh/sshd_config \
+  -e s/'#Port.*'/'Port 2222'/ \
+  -e s/'AllowTcpForwarding.*'/'AllowTcpForwarding yes'/ \
+  -e s/'GatewayPorts.*'/'GatewayPorts clientspecified'/ \
+  && ssh-keygen -A
 RUN adduser -D -s /bin/ash beagle
 ADD beagle.key /home/beagle/.ssh/authorized_keys
 RUN passwd -u beagle && \