The Babel 2 protocol spec is maintained separately.

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.