[ISSUE-95] Send replies from the right source IP address

Fixes #95

I didn't test this enough, but lets see what you have to say about it :)
I tried to keep it as simple as possible.

This has to be tested with IPv6. I guess that IPv6 is not supported yet (shouldn't be too hard to add IPv6 support though), but first lets make sure it doesn't break it.
This is kind of circular dependency on github's issue. Either drop it or use more words on why this is needed. See prev. comment.