ipv6 support

[mstebelev]

No description provided.

[mli]

many thanks for the PR! a naive question, does this PR affect the ipv4 only case? i don't have ipv6 machines at hand so cannot test it.

[mstebelev]

I tested this feature with linear.dmlc on my branch https://github.com/mstebelev/ps-lite/tree/ipv6 which is forked from v1 tag because wormhole can't be built from ps-lite/master.
It was tested on ipv6 only machines and on ipv4+ipv6 machines and it works. Don't know whether it works on ipv4 only, but i tried to make code protocol independent and likeky it works.

1. I want to push my ipv6 branch to dmlc/ps-lite repo in order to make request in wormhole to build with ipv6. How can I do it? PR can be created between existing branches
2. I don't know how to test my changes on master, may be you can check did I break something?

[mli]

sorry for the mess... i'm trying to move both wormhole/linear and wormhole/difacto to into a separate project difacto. currently i'm working on the dev branch and hope to get everything done soon (better code organization and more optimization algorithms).

it would be much better to merge ipv6 into the master branch and use difacto to instead wormhole/linear after.

[BLiuBLiu]

Could you add some full demo to show how to train the Deep Learning model in ps-lite? Such as Lenet in mnist ?