ovn: Fix receive from vxlan in ovn-controller.

ovn: Fix receive from vxlan in ovn-controller.

The changes enable source node replication in OVN for receive from vxlan
tunnels.  OVN only supports source node replication mode.  This is needed
for ovn-controller to interoperate with hardware switches.

Previously hardware vtep interaction, which uses service node
replication by default for multicast/broadcast/unknown unicast traffic
partially "worked" by happenstance.  Because of limited vxlan
encapsulation metadata, received packets were resubmitted to find
the egress port(s). This is not correct for multicast, broadcast and
unknown unicast traffic as traffic will get resent on the tunnel mesh.
ovn-controller is changed not to send traffic received from vxlan
tunnels out the tunnel mesh again.  Traffic received from vxlan tunnels is
now only sent locally as intended with obvious benefits.  This behavior is
newly documented in ovn-architecture.7.xml.

To support keeping state for receipt from a vxlan tunnel, a MFF logical
flags register flag is allocated.

As part of this change ovn-controller-vtep is hard-coded to set the
replication mode of each logical switch to source node as OVN will only
support source node replication.

Signed-off-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Justin Pettit <jpettit@ovn.org>