Support ControlMaster for UDP connections to tsshd

[jbms]

It appears that tssh does not support creating a ControlMaster socket itself, and instead just spawns openssh if a new ControlMaster socket is needed. As far as I understand, this means that there is no way to multiplex a UDP connection to tsshd via the ControlSocket protocol.

Is there a plan to implement ControlMaster support in tssh itself, such that it can be used with UDP connections?

[lonnywong]

I currently do not have the bandwidth to implement ControlMaster support. However, I would be very happy to review and merge a PR if someone contributes it.