ovsdb-server: drop all connections on read/write status change

ovsdb-server: drop all connections on read/write status change

Prior to this patch, only db change aware connections were dropped
on a read/write status change. However, current schema in OVN does
not allow clients to monitor whether a particular DB changes this
status. In order to accomplish this, we'd need to change the schema
and adapting ovsdb-server and existing clients.

Before tackling that, this patch is changing ovsdb-server to drop
*all* the existing connections upon a read/write status change. This
will force clients to reconnect and honor the change.

Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2019-July/048981.html
Signed-off-by: Daniel Alvarez <dalvarez@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>