ovn: Connect to remote lports through localnet port.

ovn: Connect to remote lports through localnet port.

Before this patch, inter-chassis communication between VIFs of same
lswitch will always go through tunnel, which end up of modeling a
single physical network with many lswitches and pairs of lports, and
complexity in CMS like OpenStack neutron to manage the lswitches and
lports.

With this patch, inter-chassis communication can go through physical
networks via localnet port with a 1:1 mapping between lswitches and
physical networks. The pipeline becomes:

Ingress -> Egress (local) -> Ingress (remote) -> Egress

The original tunneling mechanism will still be used if there is no
localnet port configured on the lswitch.

Signed-off-by: Han Zhou <zhouhan@gmail.com>
Acked-by: Russell Bryant <russell@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>