Reviewed-by: kh1

We have no way to know when the client is actually opening its ports,
so we wait until we are reasonably sure it's done.
This is not 100% safe, but should generally suffice.
(The UTFS server seems to have this logic already built in, but it does
not seem to work on Mac.)

This will help us diagnose errors.

The device configuration widget is now the only place the user
ever has to specify ports.

Wait until UTFS client has detached before starting the server.

Only tested on Linux, #ifdef'ed for now.