Improve hypriot/docker network stability

[StefanScherer]

Check if we should add this to the HypriotOS image:

See docker/docker issue 19532 "hypriot/docker network stability issues." ->
moby/moby#19532 (comment)

@gazzer82 I finally got a chance to try the workaround mentioned @StefanScherer it also did not work for me. But... I do believe I have found the solution. With many, many thanks to @aaronlehmann! He originally found the workaround here distribution/distribution#785 (comment). He has a more complete summary on moby/libnetwork#1090.

I ended up using his echo 1 > /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_be_liberal workaround.

This has me now building container images from home!

Hope this helps you and others!
Will

[StefanScherer]

reverting PR #112 with #113 as it does not work yet.