If overlay encryption is required between peers, the fast datapath
forwarder returns an error rather than aborting the process, allowing
the overlay switch to fall back gracefully to an encrypted sleeve
overlay connection.
Forward can return nil if the remote peer has HasShortID false. That
can happen if we learn about a 1.2 peer from a 1.1 peer and attempt to
connect to it.
This change just fixes the panic. HasShortID will never be set, so we'll
fall back to sleeve. But if that occurs, if can be fixed by a restart of
the affected routers.
This is mostly a matter of moving some files, changing package names,
changing some imports, and changing some type references.
We duplicate the odd constant & global var, and the intmac/macint
functions, since neither 'router' or 'mesh' nor, really,' common' are
a natural home for them.
...since the main connections only need to know about the former.
We make LocalConnection.Overlay (formerly '.forwarder') public since
the router needs access to it, and it shouldn't be doing that via a
private field.
Adam Harrison