On OVS agent, trunk extension is always loaded. If trunk plugin is not
enabled server side, we don't want to enable extension on agent side.
It will avoid declaration of RPCServer for Trunk and SubPort objects.
To effectively disable the trunk extension, let's introduce a new
parameter under [OVS] group so that an operator turn that setting off.
The default value will stay True for now to keep backward compatibility
with previous deployments.
Closes-bug: #2058712
Change-Id: I94602d5f3159d9a2d5b988c9ab6cdd20dfd4af5b
Signed-off-by: Arnaud Morin <arnaud.morin@ovhcloud.com>