ovn: Add logical port 'enabled' state.
This patch adds a new column to the Logical_Port table of the
OVN_Northbound database called 'enabled'. The purpose is to allow a
port to be administratively enabled or disabled. It is sometimes
useful to keep a port and its related configuration, but temporarily
disable it, which means no traffic is allowed in or out of the port.
The implementation is fairly non-invasive as it only required minor
changes to the logical pipeline.
Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>