Added files related to transparent tcp relay

[choksi81]

I have added files related to transparent tcp relay feature. I will briefly explain this feature:

• The server contacts the relay to open a port on its behalf and listen for client-connection.
• The relay opens up a random port from the available ports and advertises this port with the key which the server sends to it.
• The client can now open a connection with the server via the relay using the port which has been opened on the relay.
• The relay transfers all the messages between client and the server.

It is known as transparent-tcp-relay because the client side doesn't know that it is actually communicating with the relay instead of server.

There is a unit-test also which successfully checks if closing of socket during server setup is handled correctly or not.

There are few other unit-tests which I have created, but are not there in this PR. (You can find them here: https://github.com/choksi81/affix/tree/affix_transparenttcprelay_final/services/transparent_tcp_relay/tests)
They are almost(but not entirely) complete. If someone wants to complete those, they can contact me, I will explain the work I have done till now on them.

[choksi81]

Also, once this PR gets merged, the config_build will have to be updated to copy over the transparent-tcp-relay files. While updating, refer this file (https://github.com/choksi81/affix/blob/affix_transparenttcprelay_final/scripts/config_build.txt)