I don't quite understand the tradeoff that's involved, but now that
multihop requests work, this shouldn't harm, and might make more routes
feasible straight away.

This avoids overflow by expanding the range.

Thanks to Yoann Canal.

Significantly simplifies the xroute logic.

Run make EXTRA_DEFINES=-DNO_LOCAL_INTERFACE.

It is now controlled by -g.

This doesn't matter for regular Babel, but it breaks the babel-local-interface
branch, which uses a TCP socket for communicating with the GUI.