There's no longer an id on the command line, and the neigh filter has a
different semantics.

This function does nothing right now, it will be used when we learn to resend
unicast packets.

The old find_neighbour is now an internal function (f_n_no_create).

It doesn't appear to be useful, and complicates uselessly complicates matters.

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.