Support for unix domain socket forwarding #389
Description
I was trying to set up gpg agent forwarding with a dropbear ssh server and realized that while tcp port forwarding was supported, socket forwarding was not. Took a stab at an implementation here, and it is working well enough for my needs. Would you accept a PR for this? I'd be happy to address any feedback you have to make it cleaner / more robust. It's been a long time since I've done any real work in C and I'm admittedly not a security expert so I'm sure there is room for improvement.